The plasma LH concentration is believed to be reasonably steady in normal male rats. We found that LH is released in a regular pulsatile fashion. The overall mean concentration of plasma LH in normal male rats was 46.6 ± 4.4 (mean ± SEM) ng/ml. The normal male rats showed periodic LH pulses: the mean pulse amplitude was 144.4 ± 25.5 ng/ml and the inter-peak interval was 22.5 ± 2.0 min. Each pulse lasted 9.7 ± 0.8 min. When LH-RH (1 µg/kg) was injected as a bolus, the peak concentration was attained in 10-30 min reaching a peak concentration of 279.4 ± 39.6 ng/ml. Distinct pulsatile bursts of plasma LH were discernible during the period of elevated plasma LH concentration. When a higher dose of LH-RH (5 µg/kg) was administered, the LH concentration slowly increased to a peak concentration of 400.2 ± 38.7 ng/ml in 20-40 min. The pulsatile nature of the LH concentration was recognizable with distinct bursts. We have observed that: (a) normal male rats release LH in a pulsatile fashion with an approximate 20-min inter-peak interval; (b) mean LH pulses last less than 10 min, and (c) the LH pulses are visible even with elevated LH and LH-RH concentrations in the general circulation.