The invention comprises 16-methylene-5-pregnene-3b  b , 17a -diol-20-one 3-acetate, and a process for the preparation of 16-methylene steroids of the general formula &lt;FORM:0941553/C2/1&gt; wherein Z represents H or OR1 (R1 being H or acyl), R2 represents a H, b OH or b H, a OH, or =O, and X represents hydrogen or fluorine, and the corresponding 1-dehydro derivatives, which comprises treating 16-methyl-5,16-pregnudien-3b -ol-20-one or a 3-acylate thereof with an epoxidising agent (e.g. a per-acid or alkaline hydrogen peroxide) to produce the corresponding 16b -methyl-16a , 17a -oxido-5-pregnen-3b -ol or a 3-acylate thereof, and subjecting the resulting 16a , 17a -oxido compound to the following operations as appropriate and in suitable order:-  (a)  treating the 16b -methyl-16a , 17a -oxido grouping with at least a catalytic amount of a strong acid in an inert solvent to form the 16-methylene-17a -hydroxy grouping;  (b)  oxidising the 3b -hydroxy (or acyloxy)-5-ene system to a 3-keto-4-ene system;  (c)  microbiologically hydroxylating at the 11-position; said process optionally including one or more of the following operations:-  (d)  treating a 21-unsubstituted steroid with bromine or an alkaline iodine solution to form a 21-halo compound and treating this compound with an alkali metal acylate to form a 21-acyloxy group;  (e)  hydrolysing a 21-acyloxy group to form a 21-hydroxy group;  (f)  dehydrogenating with a 1, 2-dehydrogenating agent;  (g)  dehydrating a steroid containing an 11-hydroxy group to produce the corresponding 16-methylene- D 9 (11)-steroid, treating this steroid with hypochlorous or hypobromous acid to form a 16-methylene-11 b -hydroxy-9a -chloro (or bromo)-steroid, treating this compound with an alkali metal acylate to form the corresponding 16-methylene-9b , 11 b -oxido-steroid, and treating this compound with hydrogen fluoride to form a steroid of the above general formula wherein X represents fluorine and R2 is a -H, b -OH;  (h)  oxidising a steroid of the above general formula wherein X represents hydrogen and R2 represents a -H, b -OH or b -H, a -OH, or wherein X represents fluorine and R2 represents a -H, b -OH to form the corresponding 11-keto steroid.  The 16a , 17a -oxido ring may be opened with the strong acid at the stage where the 3b -hydroxy (or acyloxy)-5-ene system is present or at the stage where the 3-keto-4-ene system is present. The strong acid may be p-toluene- or benzenesulphonic acid. The oxidation step to form the 3-keto group may be carried out by the Oppenauer method, or by means of chromic acid in pyridine, or chromosulphuric acid in acetone, or by means of a cultive of the microorganism Flavobacterium dehydrogenans.  The 11-hydroxylation may be carried with microorganisms of the genus Curvularia (for 11b -hydroxylation), or of the genera Absidia, Aspergillus, Fusarium, Mucor Penicillium or Rhizopus (for 11a -hydroxylation). The dehydrogenation may be carried out using micro-organisms Bacillus sphaericus, Fusarium solani and Corynebacteria, preferably Corynebacterium simplex.  The dehydration step to form the 9(11)-unsaturation may be carried out with phosphorus oxychloride or thionyl chloride in pyridine in the case of an 11b -hydroxy compound, or with esterification, e.g. to form an 11a -organo-sulphonate, followed by basic or thermal splitting out of the corresponding acid in the case of an 11a -hydroxy compound. The oxidation of the 11-hydroxy group may be carried out with chromic acid, chromic acid and pyridine, chromic acid in acetone or hypohalous acid.  The bromination of a steroid compound containing a 3b -hydroxy (or acyloxy)-5-ene system in step (d) above gives rise to a 5,6,21-tribromo-steroid which is then treated with sodium iodide to form a 21-iodo steroid, the 5(6) double bond being reformed. Specification 880,464 is referred to.