OBJECTIVE: To confirm that hCG levels in follicular fluid and serum would be comparable between i.m. and s.c. administration of purified hCG. DESIGN: In a prospective study, serum and follicular fluid levels of hCG after an i.m. or s.c. injection of 10,000 IU of hCG were evaluated 36 hours after injection, that is, at the time of oocyte retrieval. SETTING: This study was carried out in a university-affiliated IVF program. PATIENT(S): Forty women undergoing oocyte retrieval were entered into the study at the time of egg retrieval, that is, 36 hours after hCG administration. INTERVENTION(S): S.c. or i.m. injection of hCG. MAIN OUTCOME MEASURE(S): Serum and follicular fluid concentrations of hCG were evaluated 36 hours after injection at the time of oocyte retrieval. RESULT(S): There was a significantly higher serum hCG level in the s.c. group (348.6 +/- 98 IU/L) vs. the i.m. group (259.0 +/- 115 IU/L) and a significantly higher follicular fluid hCG level in the s.c. vs. the i.m. group (233.5 +/- 85 vs. 143.4 +/- 134 IU/L). CONCLUSION(S): After purified hCG administration via the s.c. route, both serum and follicular fluid levels are greater compared with the i.m. route.