Conditions are described for conversion of testosterone into the 3-enol, 17-bis-tert.-butyldimethylsilyl ether derivative without formation of side products. The steroid is treated with tert.- butyldimethylsilylimidazole in heptane at 100 degrees C using sodium formate as catalyst. Derivatives are also formed at different rates of 3-keto-5 alpha, 3 alpha/beta-hydroxy-, 6 alpha/beta-hydroxy-, 7 beta-hydroxy-, 16 alpha-hydroxy-, 17 beta-hydroxy(sec.)- and 20 alpha/beta-hydroxysteroids, whereas hydroxyl groups in 1 beta, 7 alpha, 12 alpha/beta, 15 beta and 17 alpha(tert.) positions do not react to a significant extent. These positions are derivatized by subsequent addition of trimethylsilylimidazole , yielding mixed derivatives which are suitable for gas chromatography--mass spectrometry with selected ion monitoring. Conditions are given for conversion of some biologically important androgens, progestins and bile acids into a single form of derivative. The use of the method is illustrated by an analysis of steroids in a rat testis.