Steroidogenesis was studied in the regenerating adrenal glands of rats. There was a reduction of desoxycorticosterone (DOC), corticosterone, 18 oxy 11 desoxycorticosterone and aldosterone biosynthesis on the 10th and 20th postoperative days. The addition of DOC and progesterone to the incubation medium, or an increase in the synthesis of intermediate products under the influence of ACTH increased the steroidogenesis. This indicated that production of the main steroids could be decreased not only by a reduction in the activity of the 11, 21 and 18 hydroxylation compounds but also by a fall in the concentration of intermediate products of the synthesis at the early stages of steroidogenesis. A more marked fall of the rate of biosynthesis during the incubation period pointed to a greater dependence of the synthesis in the regenerating adrenal glands on ACTH. An increase of the desoxycorticosterone/corticosterone coefficient in the regenerating adrenal gland incubates reflects changes in the spectrum of the synthesized hormones.