Recent studies have shown that LH secretion is pulsatile and that LH pulse characteristics are affected by the prevailing steroid environment in both male and female rats. In the present study, a cell perifusion system was used to examine the effects of testosterone (T) and 17 beta-estradiol (E) on LHRH-stimulated pulsatile LH secretion. T inhibited LH secretion, increasing the EC50 for LHRH, while E stimulated secretion, lowering the EC50. Steroid effects were independent of both LHRH pulse amplitude and frequency. E also affected the pattern of LH secretion by facilitating both LHRH self-priming and desensitization to LHRH. These results show that steroids can affect pulsatile LH secretion by actions exerted at the pituitary level and that steroids can induce both quantitative and qualitative changes in LH secretion in the presence of an invariant LHRH stimulus. These results help to elucidate the mechanisms underlying steroid feedback in vivo, since reduction in pituitary responsiveness to LHRH may play an important role in T feedback, while facilitation by E of both self-priming and desensitization may serve to increase the magnitude and shorten the duration of the proestrous LH surge.