Long-acting GnRH analogs represent the standard treatment for gonadotropin-dependent precocious puberty. The aim of this study was to determine the hormonal parameters for monitoring the adequacy of depot leuprolide acetate treatment in girls with clinical and hormonal diagnosis of gonadotropin-dependent precocious puberty. Eighteen girls were treated monthly with 3.75 mg depot leuprolide acetate. Adequate hypothalamic-pituitary-gonadal axis suppression during treatment was achieved in 16 of the 18 girls according to the clinical parameters and prepubertal LH levels. In these 16 well-controlled girls, the LH peak after a classical GnRH test was compared with a single LH measurement obtained 2 h after depot leuprolide acetate administration before and during GnRH analog treatment. Before therapy, the mean +/- sd LH peak after a classical GnRH test was 18.4 +/- 11.2 IU/liter (ranging from 7-41.5 IU/liter), and it was 22.6 +/- 8.3 IU/liter 2 h after the first depot leuprolide dose (ranging from 10-35.3 IU/liter). During therapy, the mean +/- sd of LH peak after classical GnRH test was 1.4 +/- 0.6 IU/liter (ranging from <0.6 to 2.3 IU/liter), and it was 2.7 +/- 1.9 IU/liter (ranging from 0.7-6.6 IU/liter) 2 h after depot leuprolide. The LH peak after a classical GnRH test and that 2 h after depot leuprolide administration correlate significantly before and during treatment. In conclusion, we established the LH cut-off values for an adequate depot leuprolide therapy as an LH peak below 2.3 IU/liter after a classical GnRH test or below 6.6 IU/liter 2 h after depot leuprolide. The latter measurement may replace the classical GnRH test as a reliable and convenient tool for monitoring therapy in female gonadotropin-dependent precocious puberty.