We treated 23 patients with non-trophoblastic cancers with escalating doses of a synthetic vaccine consisting of the carboxy-terminal peptide of beta human chorionic gonadotropin conjugated to diphtheria toroid (CTP37), a muramyl dipeptide as an adjuvant, and squalene/mannide monooleate as a vehicle. Toxicity consisted of pain and sterile abscess formation at the injection site and of constitutional symptoms. Diphtheria toxoid hypersensitivity developed in one patient. Immunizations elicited anti-beta hCG IgG antibody which persisted for more than 10 months. Disappearance of circulating hCG present pre-immunization and tumor regressions were observed. Active specific immunotherapy with CTP37 vaccine is well-tolerated and has biological activity in patients with cancer.