The effects of ovariectomy and exogenous androgen administration on the indole and porphyrin metabolism of Syrian hamster Harderian glands were studied. Ovariectomy alone had no effect on any of the parameters analyzed. The administration of either testosterone or 5a-dihydrotestosterone increased the activity of N-acetyltransferase in the Harderian glands. However, androgen treatment failed to change the activity of hydroxyindole-O-rnethyltransferase. Melatonin content of the glands dropped 20 days after treatment with testosterone and 10 days after the administration of 5adihydrotestosterone. The porphyrin content of the Harderian glands was dramatically depressed after the administration of either androgen. It is concluded that the Harderian glands of Syrian hamsters are under an androgenic control involving 5a-dihydrotestosterone. [P.S.E.B.M. 1989[P.S.E.B.M. , Vol 1921 he Harderian glands are located in the posterior part of the orbital cavities of most of the mam-