A systematic study of transformation reactions of the genus Streptomyces with respect to the progesterone molecule was undertaken. The types of transformation reactions by different Streptomyces species were evaluated from the point of view of taxonomy. The isolates tested were divided according to the transformation types into six groups: (1) a group of species transform progesterone to 16 alpha-hydroxyprogesterone; (2) a group of species transform progesterone to 6 beta-hydroxyprogesterone; (3) a group of species transform progesterone to 6 beta, 11 alpha-dihydroxyprogesterone; (4) a group of species dehydrogenate progesterone in C1-2 position; (5) a group of species transform progesterone to 3 derivatives namely 6 beta-hydroxyprogesterone, 6 beta, 11 alpha-dihydroxyprogesterone and dehydrogenation in position C1-2; (6) a group of species with no capacity to transform progesterone into another steroid derivative. From the point of view of Streptomyces classification, the transformation reaction of progesterone fulfil all the requirements of taxonomic feature of Streptomyces. These appear to be specific properties and common to all the strains of individual Streptomyces species tested.