Marijuana use has been reported to spuriously elevate immunoreactive human chorionic gonadotropin (HCG) in the serum of patients with testicular germ cell tumors. To reinvestigate this finding, we measured serum HCG and delta 9-tetrahydrocannabinol (delta 9-THC) levels in 16 men known or suspected to be marijuana users. Eight of the serum samples had measurable levels of delta 9-THC, while eight did not. None contained immunoreactive HCG. The addition of delta 9-THC directly to pooled male serum had no effect on the HCG radioimmunoassay. These results indicate that marijuana does not artificially elevate serum HCG concentrations.