Nineteen patients with various solid tumors were treated with Corynebacterium parvum for 10 consecutive days at doses ranging from 0.5 to 6 mg/m2. Major toxic effects included rigors and cyanosis, hypertension, headache, nausea, and vomiting. Toxicity was maximal during the first 3 days of treatment and decreased or even disappeared when, on subsequent days, increasing doses of the vaccine were given. Objective tumor regressions were observed in four patients.