Seven adult male volunteers residing on a research ward received intravenous cocaine and smoked marijuana, alone and in combination, during daily experimental sessions. Following the determination of baseline cardiovascular indexes, a one gram marijuana cigarette (0-2.7% delta 9-THC w/w) was smoked. Cocaine hydrochloride (0-32 mg) was administered intravenously 13 minutes after the start of marijuana smoking. Cocaine alone produced dose-dependent increases in heart rate, while both low and high THC blood levels produced a similar increase in heart rate. Both doses of cocaine increased mean arterial pressure (MAP) similarly, while THC alone produced blood level dependent increases in MAP. Combinations of cocaine and marijuana increased heart rate above levels seen with either drug alone, with increases plateauing at nearly 50 bpm for all dose-blood level combinations. Increases in mean arterial pressure following combinations of cocaine and marijuana were equivalent to those produced by cocaine alone.