Prepuberal patterns of pituitary luteinizing hormone (LH) con-tent in male and female rats were studied using the ovarian ascorbic acid-depletion bioassay technique. Pituitary LH content increases in both sexes until 26 days of age; however, the con-tent in the female is greater than in the male. After 26 days, pituitary LH content in the female reaches a plateau until the onset of puberty, at which time a significant fall in LH is observed coincident with vaginal opening and ovulation. Pituitary LH content in the male continues to rise beyond 26 days of age, surpassing the level in the female. A peak pituitary LH content is observed in males at 60 days with a fall to final adult levels by 75 days. Although puberty (defined as the time of appearance of sperm in penile smears) occurs later in the male than in the female rat, an increase in accessory sex organ weights, suggestive of increased gonadal steroid secretions, precedes the puberal fall of LH in both sexes. Testosterone administration to 1-day-old female rats inhibits the development of cyclicity and initially produces a prepuberal pattern of pituitary LH content similar to that of the male. However, after the appearance of the polycystic ovary syndrome at 40 days of age, a plateau is reached in pituitary LH content, and puberal changes characteristic of either the normal male or female are never observed.