On the basis of the results of morphological and histochemical study of two malignant granulosa cell tumours removed in women with the virile syndrome the author came to the conclusion that theca-tissue was a necessary structural component of such tumours. Theca cell component can be expressed to a different extent, but its cells, in contrary to the cells of the prevailing ganulosa cell component of such tumours, possessed a high enzymatic activity providing the processes of the steroid hormone biosynthesis, and contained lipids intimately connected with these processes. These data permit to regard the theca cell component of malignant granulosa cell tumours as the main source of hormones produced by such tumours.