Commercially available radioimmunoassay (RIA) kits for human follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were adapted for quantitation of these hormones in serum from bottlenosed dolphins (Tursiops truncatus). Serum samples from over 160 wild and 70 captive animals were assayed in order to determine basal concentrations of FSH and LH in these animals, as well as to detect possible differences between various groups. Mean FSH and LH levels for all animals were 0.22 +/- 0.08 and 0.37 +/- 0.18 ng/ml, respectively. Although wild animals had higher FSH and LH levels than captive ones, the differences were not statistically significant (P less than 0.07). However, both FSH and LH were significantly (P less than 0.01 and P less than 0.05, respectively) elevated in females when compared to males. Adults and peripubescent animals had significantly (P less than 0.01) higher LH levels than did juveniles. Among wild animals, serum concentrations of FSH and LH reflected seasonal differences. Samples obtained in early summer (Gulf of Mexico population) contained significantly (P less than 0.01) higher concentrations of FSH and LH than samples obtained in the fall (Indian River, Florida population). Both FSH and LH were significantly elevated in samples from confirmed pregnant animals as compared to the overall mean and to a sample from a confirmed nonpregnant female. Our observations indicate that these RIAs can reliably detect serum FSH and LH from bottlenosed dolphins and represent the first quantitation of these hormones in cetaceans.