The invention comprises steroid compounds of the general formulae <FORM:0886861/IV (b)/1> <FORM:0886861/IV (b)/2> <FORM:0886861/IV (b)/3> wherein X represents hydrogen, fluorine, chlorine or bromine, R represents hydrogen or an acyl group, including a phosphate group, Y represents a keto or hydroxy group, Z represents a group convertible to a keto group by acid hydrolysis, and the dotted line in the 1 (2) position represents the presence of an optional double bond, and a process that comprises reacting 16a -methylcortisone with formaldehyde under acidic conditions to form 17a ,20,20,21-bismethylenedioxy-16a -methyl-3,11-diketo-4-pregnene, protecting the 3-keto group of this compound by converting it to a group convertible to a keto group by acid hydrolysis, epoxidising the 3-protected keto compound to form a 3-(protected keto)-17a ,20,20, 21 - bismethylenedioxy - 5, 6 - epoxy - 16a - methyl - 11-keto-pregnane, reacting this compound with formic acid to produce a mixture of 17a ,20,20,20-bismethylenedioxy - 17a - methyl - 6a - formlyoxy - 5-hydroxy-3,11-diketo-pregnane and 17a ,20,20,21-bismethylenedioxy - 16a - methyl - 5 - formyloxy - 6a -hydroxy-3,11-diketo-pregnane, treating this mixture with a base such as aqueous alkali metal hydroxide, to form 17a ,20,20,21-bismethylenedioxy - 16a - methyl - 3, 6, 11 - triketo - allo - pregnane, protecting the 3-keto group of this compound by converting it to a group convertible to a keto group by acid hydrolysis to form a 3-protected keto-a 17,20,20,21-bismethylenedioxy-16a -methyl-6, 11-diketo-allopregnane, reacting this compound with a methyl Grignard reagent to for a 3-protected keto-17a ,20,20,21-bismethylenedioxy - 6a , 16a - dimethyl - 6b - hydroxy - 11 - keto allopregnane, and reacting this compound with a dehydrating agent such as thionyl chloride in pyridine, to form a 3-protected keto-17a ,20,20, 21 - bismethylenedioxy - 6, 16a - dimethyl - 11 - keto-5-pregnene, with the optional further step of reducing the 11-keto group to an 11b -hydroxy group, e.g. with lithium aluminium hydride, to form a 3-protected keto-17a ,20,20,21-bismethylenedioxy - 6, 16a - dimethyl - 11b - hydroxy - 5 - pregnene, with the optional further step of subjecting the 3-protected keto-17a ,20,20,21-bismethylenedioxy-6,16a -dimethyl-11-(keto or b -hydroxy)-5-pregnene to acid hydrolysis, e.g. with p-toluenesulphonic monohydric in anhydrous acetone, to form 3-keto-17a ,20,20,21-bismethylenedioxy-6a ,16a -dimethyl-11-(keto or b -hydroxy)-4-pregnene, with the optional further step of hydrolysing the last mentioned compound with aqueous organic acid to produce 6a ,16a -dimethyl - cortisone or 6a , 16a - dimethyl - hydro - cortisone, with the optional further steps of acylating the 6a ,16a -dimethyl-hydrocortisone to form the corresponding 21-acylate, reacting the 21-acylate with a dehydrating agent, e.g. phosphorus oxychloride or methane sulphonyl chloride, to produce a 6a ,16a -dimethyl-17a -hydroxy-21 - acyloxy - 3, 20 - diketo - 4, 9 (11) - pregnadiene, and brominating this compound to form 9a - bromo - 6a , 16a - dimethyl - 11b , 17a - di - hydroxy - 21 - acyloxy - 3, 20 - diketo - 4 - preg - nene, with the optional further steps of reacting the 9a -bromo compound with anhydrous potassium acetate in ethanol to form a 6a ,16a -dimethyl-9,11 - epoxy - 17a - hydroxy - 3, 20 - diketo - 21 - acyloxy-4-pregnene and treating the 9,11-epoxy compound with hydrogen fluoride to form a 6a , 16a - dimethyl - 9a - fluoro - hydrocortisone 21-acylate which may be hydrolysed to the corresponding 21-hydroxy compound, and with the optional further step of oxidising the 6a ,16a -dimethyl-9a -fluoro-hydrocortisone or the 21-acylate thereof with chromium trioxide in pyridine to form 6a ,16a -dimethyl-9a -fluoro-cortisone or its 21-acylate. The invention also includes processes for the preparation of 21-hydroxy-1,4-pregnadienes of the above general formula by reducing the corresponding 4-pregnene compounds or 21-acylates thereof with the dehydrogenating activity produced by growing Schizomycetes or Bacillus sphaericus micro-organisms, and for the preparation of the 21-hydroxy- and 21-acylate-1,4-pregnadiene compounds of the above general formula by reducing the corresponding 4-pregnene compounds with selenium dioxide. The group at the 3-position which is convertible to keto by acid hydrolysis may be a cyclic ketal group such as an ethylenedioxy, ethylenedithioketal or ethylene hemithioketal group, a cyclic amine group, a pair of univalent groups such as a non-cyclic grouping-particularly dimethylketal or dimethylthioketal, or a single univalent group such as an enol ether group in which case there is an additional double bond in the 3-position. Detailed examples are given. Specification 877,085 is referred to.