BACKGROUND Low concentrations of serum LH and/or oestradiol (E(2)) in girls with early physical signs of precocious puberty pose a diagnostic challenge. OBJECTIVE To assess the diagnostic value of the leuprolide stimulation test in female precocious puberty. METHODS Retrospective Chart Review. METHODS Outpatient clinic. METHODS Thirty-nine girls, 6.9 (1.4) years, with premature stage II-III breast development, with or without pubarche, underwent stimulation testing with subcutaneous leuprolide (20 microg/kg) with the following hormonal measurements in serum: FSH, LH, oestradiol at baseline; FSH and LH at 1 and 2 h; oestradiol at 24 h. Twelve girls with isolated pubarche were also tested with leuprolide. METHODS A pubertal hormonal pattern was defined as at least one of the following: a baseline serum level of LH > or = 0.3 U/l, a baseline oestradiol > or = 37 pmol/l (10 ng/l), a stimulated (peak) LH > or = 5.0 U/l, a stimulated oestradiol > or = 184 pmol/l (50 ng/l) to leuprolide. The hormonal response was related to the clinical course during a period of observation of at least 6 months. RESULTS Following leuprolide stimulation, the hormonal response was concordant with pubertal progression (n = 23) or lack thereof (n = 16) in all children. At baseline, pubertal serum concentrations of LH and/or oestradiol were associated with pubertal progression in all, while serum prepubertal LH and/or oestradiol concentrations were associated with pubertal progression in approximately 50% of the patients. CONCLUSIONS In girls with early clinical signs of precocious puberty and low serum concentrations of LH and oestradiol in random samples, the LH and oestradiol responses to leuprolide stimulation accurately predict pubertal progression.