Water-soluble derivatives of cyclic amidines which have an affinity for cellulosic fibres, and have no tinctorial properties but exhibit a blue fluoresence in daylight and ultra-violet light, are prepared by sulphonating, or condensing with an N-methylol compound of a sulphonated carboxylic acid amide, a cyclic amidine of the general formula <FORM:0588972/IV/1> in which A represents an aromatic nucleus which may contain substituents and of which two vicinal carbon atoms are attached to the two nitrogen atoms of the amidine, R1 represents hydrogen or an alkyl, aryl or aralkyl residue, and R represents a radical containing directly attached to the m -carbon atom a carbon atom which is either directly attached to a hydrogen atom or is a member of a ring, and containing an uninterrupted series of at least 4 conjugated double bonds which start with the carbon atom directly connected to the m -carbon atom, and of which at least two are in a ring. In a modification, water-soluble derivatives are obtained by introducing at least one quaternary ammonium group by first condensing the cyclic amidine with a halogen-carboxylic acid N-methylolamide (e.g. as described in Specification 533,155) and then causing a tertiary amine to combine additively with the product so obtained, or by condensing the cyclic amidine with the addition product of a tertiary amine and a halogen-carboxylic acid N-methylolamide. In a further modification, a water-soluble derivative is obtained, when the cyclic amidine has a hydrogen atom attached to an oxygen or nitrogen atom, by treating the cyclic amidine with an alkylene oxide to introduce a polyglycol ether residue. Another modification is described in which an amino cyclic amidine in which R represents a styryl group is condensed with a sulphonated benzoic acid halide. The following examples are included: (1) 6-amino - 2 - (31 - aminostyryl) - benzimidazole (prepared from 6-nitro-2-methyl-benzimidazole and 3-nitrobenzaldehyde followed by reduction) is condensed with anisoyl chloride, and the 6 - anisoylamino - 2 - (31 - anisoylaminostyryl)-benzimidazole formed is sulphonated. (2) o-Phenylenediamine is condensed with fumaric acid (maleic acid or maleic anhydride) and the product sulphonated; (3) 1,2-nitro-aminobenzene is reacted with fumaric acid dichloride and the fumaric acid di-(o-nitranilide) treated with granulated tin in the presence of acetic and hydrochloric acids; the amidine so formed is then sulphonated; (4) a b -di-(benzimidazyl-2)-ethylene obtained as in (2) is reacted with benzyl chloride, and the a b -di-(N-benzyl-benzimidazyl-2)-ethylene sulphonated; (5) a b -di-(isopropylbenzimidazyl - 2) - ethylene is prepared from fumaric acid and isopropyl-phenylenediamine-1,2 (obtained by isopropylation of 1,2-dichlorobenzene followed by replacement of the chlorine atoms by amino groups) and then sulphonated. A similar compound is made from 5-chloro-1,2-diaminobenzene and fumaric acid; (6) dibenzimidazyl-2,21 is sulphonated; (7) a b -di-(benzimidazyl-2)-ethylene is sulphonated; (8) 2-methyl-benzimidazyl is condensed with sodium benzaldehyde - 2,4 - disulphonate; (9) o-phenylenediamine is condensed with terephthalic acid and the 1,4-di-(benzimidazyl-21)-benzene so obtained is sulphonated. The sulphonated 1,2-di-(benzimidazyl-21)-benzene is obtained by a similar process; (10) 1-methoxy-3,4-diaminobenzene is condensed with terephthalic acid and the 1,4-di(61-methoxy-benzimidazyl - 21) - benzene so obtained is sulphonated. Sulphonated 1,4-di-(61-chlorobenzimidazyl-21)-benzene is obtained similarly from 1-chloro-3,4-diaminobenzene; (11) 1,4-di - (benzimidazyl - 21) - 2 - chlorobenzene is obtained from 1,2-diaminobenzene and chloroterephthalic acid, and then sulphonated; (12) 2,5 - di - (benzimidazyl - 21) - furane is obtained by condensing furane 2,5-carboxylic acid with 1,2-diaminobenzene, and then sulphonated; (13) 6-amino-2-(styryl)-benzimidazole is reacted with benzoyl chloride-3-sulphonic acid in pyridine; (14) 2-methyl-benzimidazole is condensed with terephthalic anhydride and the product sulphonated; (15) 2-styrylbenzimidazole dissolved in sulphuric acid monohydrate is reacted with N-methylolchloracetamide and then treated with pyridine; (16) a b - di - (benzimidazyl - 2) - ethylene dissolved in sulphuric acid monohydrate and reacted with the addition product of trimethylamine and methylolchloracetamide; (17) a a 1-dimethyl-benz-di-imidazole is condensed with benzaldehyde and the product sulphonated; (18) bleached cotton yarn is whitened by treatment with an aqueous solution of the sodium salt of sulphonated a b -di-(benzimidazyl-2-ethylene or of the quaternary compound of example (16); (20) the sodium salt of sulphonated a b - di - (benzimidazyl - 2) - ethylene is introduced into a viscose solution intended for the manufacture of films or threads; (21) cotton fabric dyed with Direct Scarlet WS is printed with a discharge paste and subsequently treated with a solution of the sodium salt of sulphonated a b -di-(benzimidazyl-2)-ethylene; (22) mercerized cotton fabric printed in a two-colour design is treated with a solution of a sodium salt of sulphonated a b -di-(benzimidazyl-2)-ethylene; (24) bleached cotton yarn is treated in a bath containing the sodium salt of sulphonated 1,4-di-(61-methoxy-benzimidazyl-21)-benzene. Samples furnished under Sect. 2 (5) comprise (1) the sodium salt of sulphonated a b -di-(N-phenyl-benzimidazyl-2)-ethylene obtained by sulphonating the base made by condensing 2-amino-diphenylamine with fumaric acid in the presence of HBr and then adding ammonia, and (2) the product obtained by heating a b -di-(benzimidazyl-2)-ethylene with ethylene oxide and dioxane. The Specification as open to inspection under Sect. 91 comprises also examples in which (a) a b -di-(benzimidazyl-21)-ethane is condensed with benzaldehyde and the product sulphonated, and (b) a b -di-(benzimidazyl-21)-ethane is condensed with sodium benzaldehyde-2,4-disulphonate. This subject-matter does not appear in the Specification as accepted.