Objective: The LH response of pituitary gland to gonadotropin-releasing hormone (GnRH) stimulation is not well defined in patients with mutant β-subunit (Trp<sup>8</sup> to Arg<sup>8</sup> and Ile<sup>15</sup> to Thr<sup>15</sup>). Here we compared the relative activities and dynamics of LH secretion in patients with wild-type and variant LH following injection of GnRH. Methods: A GnRH stimulation test was performed in 33 patients with ovulatory disorders (patient group) and 29 women with normal ovulatory cycles (control group) heterozygous for the variant LHβ allele. Blood samples were obtained up to 120 min after GnRH injection. Serum LH response was determined by comparing the results of LH immunoassays using a monoclonal antibody that recognizes wild-type LH only with those of another assay using a polyclonal antibody that recognizes equally both variant and wild-type LH (total LH). The ratio of variant LH to total LH (LH ratio) was used to determine the serum LH status. Results: The LH ratio in the control group showed the peak 15 min after GnRH injection, while that in the patient group showed the peaks 30–60 min after injection. The LH ratio in the patient group at 120 min after injection was significantly lower than that in the control group. The percent increases in LH ratio in both groups showed the peak 15 min after injection. The patient group had significantly lower changes of LH ratio at 15, 60, 90 and 120 min after GnRH injection compared with that in the control group. Conclusion: Differences in circulatory kinetics of the two types of LH may explain the differences in LH function between patients with ovulatory disorders and women with normal ovulatory cycles.