The effectiveness of LHRH agonist therapy in the management of central precocious puberty (CPP) is dependent upon suppression of LH secretion from the pituitary. The intravenous (IV) LHRH stimulation test is the gold standard for evaluating LH suppression; LHRH agonist dose and frequency are considered appropriate when LH levels are suppressed in response to IV LHRH. LHRH is administered intravenously and 3 blood samples drawn over 60 minutes for LH measurement. A subcutaneous (SQ) LHRH injection with a single venipuncture for LH measurement 40 minutes later can be used to detect elevated LH levels in the diagnosis of CPP. We hypothesized that this rapid, less expensive SQ LHRH test would also be effective at assessing LH suppression in children receiving an LHRH agonist for CPP. 11 children (9 female) participated. Each child was receiving leuprolide acetate (10 monthly IM Lupron Depot. 1 daily SQ Lupron) to suppress central puberty (8 idiopathic, 2 growth hormone deficiency + accelerated puberty, 1 porencephalic cyst). We performed 21 comparisons of the IV and SQ LHRH stimulation tests over a 1 year period. Each subject had a SQ LHRH test performed 1 month before or 1 month after their normally scheduled(every 6 months) IV LHRH test (test order determined randomly). Dose or frequency of Lupron was not changed between the 2 tests. Tests were performed immediately before receipt of the monthly Lupron Depot injection. The IV test consisted of LHRH 100 ug/m2 with LH levels at 0, 30 and 60 minutes, in contrast to a standard SQ dose of 100 ug LHRH with a single LH level 40 minutes later. The peak LH level after IV LHRH was compared to the single LH level after SQ LHRH. There was a significant correlation in LH levels obtained with the SQ and IV LHRH tests (r = 0.88, p<0.0001). With LH suppression defined as peak LH <2 IU/L, there was concordance between the IV and SQ tests in 20/21 comparisons (17 suppressed). In one case, the SQ test indicated suppression (LH 1 IU/L) while the IV did not (peak LH 2 IU/L). However, the next IV LHRH test showed complete suppression (LH < 1 IU/L) even though the Lupron dose and frequency were not changed. These data indicate that the rapid single-sample SQ LHRH stimulation test can be used to assess LH suppression in evaluating adequacy of LHRH agonist therapy for central precocious puberty.