Pubertal development preceding menarche in normal girls having menarche at a relatively early age (11.3-12.9 years) was compared with the development of girls having menarche later (13.0-14.9 years of age). Eighty-four premenarcheal girls, 7.3-14.3 years old, were examined and their age at menarche was recorded during this longitudinal study. Girls with early menarche had a larger increase in serum oestradiol at about 10 years of chronological age, and after that age the concentrations remained higher than in girls having later menarche. Serum FSH concentrations tended to be slightly higher at the onset of puberty in the former group, even before differences in serum oestradiol concentrations were observed. Pubertal development was faster in girls having early menarche, as indicated by the significantly shorter time from both breast and public hair stage 2 to menarche. This rapid sequence can be related to the higher oestradiol levels. A dissociation between gonadarche and adrenarche was evident. The oestradiol/dehydroepiandrosterone (DHEA) ratio was higher in girls developing early menarche. Around the onset of puberty (9.0-11.5 years of age) there was a complete lack of correlation between serum DHEA concentrations and age at menarche, whereas serum FSH and oestradiol concentrations displayed strong correlations with age at menarche. The present data support the view that girls with early menarche have a more profound decrease in the sensitivity of the hypothalamic-pituitary unit to the negative feed-back of circulating steroids.