Plasma profiles of luteinizing hormone (LH), testosterone (T) and estradiol (E2) were determined in 5 mature rams during the primary breeding season (Sept.) and again when breeding activity was low (May). Blood samples collected every half hour for 24 h during Sept. or May showed that LH was released into the general circulation as distinct peaks. Although this secretory pattern was not the same for all rams, and seasonal differences were noted in certain individuals, an inherent rhythm probably persists within each ram. With the exception of 1 ram in Sept., obvious T peaks were preceded by LH peaks greater than 2 ng/ml (LH-T interval < 60 min). Season had no effect on the number and magnitude of LH peaks or on the mean concentrations. Basal levels of LH were higher (P < 0.01) in Sept. than in May. Seasonal differences in peripheral T levels were more dramatic with mean baseline, and peak concentrations elevated (P < 0.01) during the fall. The number of T peaks, like those of LH, was not affected by season. Large variations in circulating levels of E2 made any possible relationship between this hormone and LH or T difficult to identify. A diurnal or seasonal rhythm could not be established for E2 in this study. Seasonal differences occur in secretory patterns of LH and T, and a cause and effect relationship between these 2 hormones exists. Under conditions of this study, neither a consistent relationship between E2 and LH or T, nor a seasonal difference in mean E2 levels, was apparent.