AbstractThe histochemistry of lipids, Δ5‐3β‐, 20α and 17β‐hydroxy‐steroid dehydrogenases, glucose‐6‐phosphate and isocitrate dehydrogenases, NADH and NADPH‐diaphorases and acid phosphatase has been studied in the ovary of the cyclic hamster. None of the enzymes studied was present in the preantral follicles on day 1 (day of ovulation) or any day of the 4‐day cycle. With the development of antral follicles (on day 3) a few fine lipid droplets appeared in the granulosa cells. The theca interna exhibited moderate amounts of NADH‐diaphorase, Δ5‐3β‐HSDH, 17β‐HSDH and slight NADPH‐diaphorase, G‐6‐PDH and ICDH, whereas the granulosa cells of antral follicles showed weak Δ5‐3β‐HSDH, NADH‐diaphorase and moderate 17β‐HSDH but intense NADPH‐diaphorase, G‐6‐PDH and ICDH activities. All enzyme activities in both theca and granulosa became more pronounced on proestrus (day 4).In the corpora lutea (CL) all the above enzymes were present on day 1 and increased on day 2, followed by a rapid decline on days 3 and 4. Lipids were sparsely represented in CL on days 1 and 2 but showed marked accumulations on days 3 and 4. Likewise, acid phosphatase increased on days 3 and 4. The enzyme 20α‐HSDH was not detectable in the CL.The interstitium showed moderate amounts of lipids, Δ5‐3β‐HSDH and NADH‐diaphorase while 17β‐HSDH, NADPH‐diaphorase, G‐6‐PDH and ICDH were only weakly present. There were no appreciable changes in the lipid and various enzymes in the interstitium throughout the cycle except for Δ5‐3β‐HSDH which increased slightly on the afternoon of day 4. Acid phosphatase was not detected in appreciable amounts in the interstitium throughout the cycle.These findings suggest that preantral follicles are unlikely to contribute to steroidogenesis. The antral follicles are the principal source of estrogen, with the granulosa being the major site of synthesis. The interstitium can serve as a major source of progesterone (P) while the theca interna and granulosa cells of antral follicles may form additional sites for P synthesis on the afternoon of day 4. The CL in the hamster are very short‐lived and steroidogenesis in them may proceed beyond the synthesis of progesterone. The present findings are correlated with the steroid levels