In non-pregnant goats, appreciable amounts of testosterone (2.1 ng/g) and 5 alpha-dihydrotestosterone (DHT, 0.8 ng/g) were present in the corpus luteum on Day 12 of the oestrous cycle. Significant (P less than 0.01, N = 18) veno-arterial concentration differences of testosterone were found across ovaries bearing corpora lutea. No such difference in testosterone concentration occurred across ovaries without corpora lutea (P greater than 0.5, N = 12). Increased peripheral plasma concentrations of testosterone and DHT occurred at the start of luteal regression, as monitored by progesterone concentration, and before the day of oestrus. Subcutaneous injections of spironolactone (10 mg/kg/day) in peanut oil between Days 10 and 20 of the oestrous cycle inhibited the increase in testosterone and DHT concentrations and delayed luteolysis and oestrus. It is suggested that aromatization of testosterone to oestrogens is needed for luteal regression and expression of oestrus in goats.