Pituitary reactivity to GnRH, characteristic of polycystic ovarian disease (PCOD), has been attributed both to a primary ovarian cause and to hypothalamic-pituitary dysfunction. If the heightened pituitary reactivity characteristic of PCOD patients is secondary to chronic anovulation, ovulatory cycles should produce changes in the LH to FSH ratio and reduce the augmented response to GnRH. In a randomized crossover study of 10 women with PCOD, GnRH (100 μg) was injected iv on the fifth day of 2 consecutive cycles, 1 of them following anovulation and progesterone withdrawal bleeding and the other following an induced ovulatory cycle. Mean basal plasma 17β-estradiol, progesterone, and FSH levels were similar after ovulatory and anovulatory cycles. However, mean basal serum testosterone (P < 0.05) and LH (P < 0.01) levels were significantly lower, as were LH levels 30, 60, and 90 min (P < 0.01) and FSH levels 60 and 90 min (P < 0.05) after GnRH injection, after an ovulatory cycle than after an anovulatory cycle. The pituitary response to GnRH in those PCOD patients, therefore, was more normal after an ovulatory cycle than after an anovulatory cycle. We conclude that the heightened pituitary reactivity characteristic of PCOD patients is associated with chronic anovulation.