Organ indices and hepatic aryl hydrocarbon hydroxylase (AHH) were measured periodically from before gonad maturation to post-spawning on cunners (Tautogolabrus adspersus) (a) maintained in captivity, (b) maintained in captivity and treated continuously with 0.3-0.8 ppm crude oil accommodated in seawater and (c) sampled directly from the field population. Total (AHH) activity in field-sampled fish (normalized to 100 g body weight) decreased 166-fold in males and 155-fold in females from maximal values before gonad maturation to minimum values two weeks following spawning. Inducibility of AHH was suppressed during the period of minimum AHH activity but returned about 3 weeks after the end of spawning. Maximal mean AHH induction by exposure to crude oil observed during the study was 5.8-fold in males and 7.5-fold in females. Captive fish had smaller gonads in both sexes and reduced liver size in females relative to fish caught immediately before sampling. Petroleum exposure further inhibited the normal increase in gonad size in both sexes relative to an unexposed fish in addition to the inhibition due to captivity alone. Captive fish did not feed well and decreased in condition index; the oil exposed group was more affected than the control captive group.