The cardiovascular effects of prostaglandins (PG) E2 and F2α administered by different routes were studied in 22 normal healthy male and female volunteers. Rapid intravenous injection of 100 μg or more of PGE2 or slow continuous infusion of 0·8 μg/kg/min PGE2 increased the heart rate and produced a fall in blood pressure. Similar effects were produced with 5 mg PGE2 injected either intramuscularly or subcutaneously. In contrast, a single intravenous infection of 500 μg PGF2α raised the arterial blood pressure, but intravenous infusion of up to 4 μg/kg/min PGF2α or subcutaneous and intramuscular injections of 20 mg PGF2α had no effect on the cardiovascular system.