One hundred twenty patients about to receive their first treatment with potentially nauseant cancer chemotherapy were randomized to one of six antiemetic treatments: (1) no treatment; (2) placebo; (3) prochlorperazine (PCPZ), 10 mg; (4) delta 9-tetrahydrocannabinol (THC), 5 mg; (5) THC, 10 mg; (6) THC, 15 mg. Four doses of each medication were given orally at 4-hour intervals starting 2 hours before chemotherapy. A study nurse was responsible for both objective (nurse) and subjective (patient) symptom questionnaires. Serum levels were obtained at intervals for cross-reacting cannabinoids. Physiologic measurements including intraocular pressure (IOP), blood pressure, and pulmonary function were also recorded. In summary, the patients were remarkably free of adverse physiologic effects. All intraocular pressures before and after treatment were within the normal range, although a surprising statistically significant increase in IOP occurred in the group receiving 5 mg THC.