The influence of elevated environmental temperatures upon plasma levels of luteinizing hormone (LH) was evaluated in eight 16-mo-old Angus heifers subjected to a control temperature regime (17-21°C diurnal variation) and an experimental temperature regime (21-34°C diurnal variation). The experimental regime significantly (p < 0.05) decreased preovulatory and basal LH levels based upon 0800 and 1600 h samples. Mean preovulatory LH levels were 6.4 ng/ml (SEM = 1.9, n = 16) in the control environment and 2.7 ng/ml (SEM = 0.9, n = 16) in the experimental regime. Comparable values for basal levels were 0.8 ng/ml (SEM = 0.03, n = 176) and 0.68 ng/ml (SEM = 0.02, n = 176). Seven of eight animals exhibited an LH surge (≥4.0 ng/ml) while exposed to the control environment compared to only three of eight at the experimental environment.