The neurotransmitter histamine (HA) may participate in the regulation of some pituitary hormones. We, therefore, investigated the effect of HA (50 µg/kg body weight/h, infusion 0–240 min) on basal and thyrotropin-releasing hormone (TRH) and luteinizing hormone releasing hormone (LH-RH) stimulated prolactin (PRL) and LH secretion in 5 normal women during the early follicular and the luteal phases of the same menstrual cycle. HA had no effect on the basal secretion of the two hormones. However, the PRL response to 200 µg TRH during the HA infusion was significantly increased compared to the response to a saline control infusion during the early follicular phase (peak responses were 1,902 ± 398 vs. 1,228 ± 230 µlU/ml, p < 0.025) and during the luteal phase (peak responses were 2,261 ± 335 vs. 1,647 ± 245 µlU/ml, p < 0.05). HA potentiated the LH response to 100 µg LH-RH during the early follicular phase (peak responses were 37.1 ± 4.9 vs. 26.9 ± 4.5 mlU/ml, p < 0.05) and during the luteal phase (peak responses were 79.3 ± 22.5 vs. 50.7 ± 11.4 mlU/ml, p < 0.025). We, therefore, found HA to have a potentiating effect on TRH/LH-RH-stimulated PRL and LH secretion in women. The results are similar to our previous findings in men, although the potentiating effects of HA were h