The current study was designed to compare blood and cerebrospinal fluid (CSF) pharmacokinetic characteristics of two forms of human chorionic gonadotropin (hCG): Pregnyl(R), derived from human urine, and Ovitrelle(R) a recombinant form. Two separate groups, each with six older male human subjects, were dosed with either form of the drug at 10,000 IU intramuscularly (IM), and followed over a 36-hour period. No significant difference in the serum level of hCG was observed for either preparation of hCG (Peak serum conc.: 316 +/- 53 vs. 270 +/- 60 at 12 hours, 311 +/- 38 vs. 321 +/- 60 IU/l at 24 hours; AUC: 10,053 +/- 1,268 vs. 8,793 +/- 1,768, Pregnyl and Ovitrelle, mean +/- SD, respectively). Additionally, both forms of circulating hCG distributed to the central nervous system (CNS) as manifest by an increased number of subjects whose CSF samples showed detectable levels of hCG in their CSF over a 36-hour period. Similarly, there was no significant difference between the two forms when distribution to the CSF was compared at 36 hours (2.0 and 1.2 IU/l; range 1.9 - 2.1 and 1 - 1.4 IU/l for Pregnyl and Ovitrelle, resp.). This preliminary study in normal human volunteers suggests that the two forms of hCG tested, Ovitrelle(R) and Pregnyl(R), when administered IM, distribute in a similar fashion into the circulation and CSF. Consequently, we conclude that these two drugs demonstrate no statistical significant difference with respect to the CSF.