Twenty-seven girls aged 8 to 18 were studied in a longitudinal prospective fashion. Serum samples were collected at 6 month intervals up to 4 years and radioassayed for hormones of pituitary, ovarian, and adrenal origin. A progressive elevation of luteinizing hormone (LH), follicle-stimulating hormone/FSH), estradiol (E2), dehydroepiandrosterone (DHA), and androstenedione (delta4) occurred during puberty and continued until menarche. The onset of puberty occurred concomitantly with an elevation of estrone (E1) dehydroepiandrosterone (DHA), dehydroepiandrosterone sulfate (DHAS), and 17-hydroxyprogesterone (17-OH-P). Prolactin (Prol) and progesterone (Prog) concentrations did not change during puberty until after menarche. After menarche, levels of LH and FSH were comparable with menstruating adult females. Concentrations of E2 and Prog were lower during the second half of the cycle among most regularly menstruating subjects than expected during the luteal phase. LH and Prog levels indirectly suggest that ovulation occurs in a few girls within months after menarche.