GnRH receptor mutations have recently been identified in a small number of familial cases of nonanosmic hypogonadotropic hypogonadism. In the present report we studied a kindred in which two sisters with primary amenorrhea were affected with GnRH deficiency due to a compound heterozygote mutation (Gln(106)Arg, Arg(262)Gln) and performed extensive phenotyping studies. Baseline patterns of gonadotropin secretion and gonadotropin responsiveness to exogenous pulsatile GnRH were examined in the proband. Low amplitude pulses of both LH and free alpha-subunit (FAS) were detected during 24 h of every 10 min blood sampling. The proband then received exogenous pulsatile GnRH i.v. for ovulation induction, and daily blood samples for gonadotropins and sex steroids were monitored. At the conventional GnRH replacement dose for women with hypogonadotropic hypogonadism (75 ng/kg), no follicular development occurred. At a GnRH dose of 100 ng/kg, the level and pattern of gonadotropin secretion more closely mimicked the follicular phase of normal women; a single dominant follicle was recruited, and an endogenous LH surge was elicited. However, the luteal phase was inadequate, as assessed by progesterone levels. At a GnRH dose of 250 ng/kg, the gonadotropin and sex steroid dynamics reproduced those of normal ovulatory women in both the follicular and luteal phases, and the proband conceived. The FAS responses to both conventional and high dose GnRH were within the normal range. The following conclusions were made: 1) Increased doses of GnRH may be used effectively for ovulation induction in some patients with GnRH receptor mutations. 2) Higher doses of GnRH are required for normal luteal phase dynamics than for normal follicular phase function. 3) Hypersecretion of FAS in response to exogenous GnRH, which is a feature of congenital hypogonadotropic hypogonadism, was not seen in this patient with a GnRH receptor mutation.