Serum concentrations of LH, FSH, testosterone and estradiol were measured in 6 subjects with the complete form of testicular feminization who ranged in age from 0.5–21.0 yr. The 3 postpubertal subjects showed LH levels elevated above the age-matched eugonadal male range, while serum FSH, testosterone and estradiol levels were within normal male limits. The 3 prepubertal subjects showed normal or only slightly elevated LH and FSH concentrations. Serial LH, FSH and testosterone determinations over 1 month in the 21-yr-old subject showed no cyclic variation. Stilbestrol, but not fluoxymesterone, suppressed gonadotropinand testosterone levels in this subject. In 4 subjects, including the 0.5 yr old, castration resulted in a marked increment in FSH levels and a further rise in LH levels. Postcastration studies showed no gonadotropin suppression by dihydrotestosterone propionate, but significant suppression by testosterone propionate; similar effects were seen in 4 young adult castrate “controls”. Gonadotropin suppression following testosterone administration correlated with a rise in serum estradiol concentrations. The ready suppression of gonadotropin levels by stilbestrol and the aromatizable androgen testosterone, together with the absence of the usual suppression by fluoxymesterone suggests that intesticular feminization the hypothalamic-pituitary unit, like other tissues, is responsive to estrogens but not androgens. The inability of dihydrotestosterone to suppress gonadotropin levels in testicular feminization or in castrate males suggests that the mechanism of this androgen resistance is not a failure to convert testosterone to dihydrotestosterone.