The effects on severe arterial ischaemia of infusions of Prostaglandin E1 (PGE1) a vasodilator and inhibitor of platelet aggregation, were studied in 49 patients (aged 17-80). Criteria for patient selection included rest pain and/or digital ulceration and gangrene secondary to predominantly small vessel disease. PGE1 was infused at a low (6 ng/kg/min), intermediate (10 ng/kg/min) or high (14 ng/kg/min) dose rate via a central venous cannula on 52 occasions without serious side effects. Doppler studies, pulse volume recordings and infra red radiometry were used to quantify the clinical effects. Improvements in digital perfusion were demonstrated by increased pulse volume amplitude (7.1 +/- 1.1 to 21.6 +/- 2.7 mm mean +/- SEM) which remained significantly raised at 6 weeks (14.2 +/- 2.9 mm; P = less than 0.001 paired t test). Infra red digital temperatures were also significantly raised 6 weeks post infusion (27.2 +/- 0.6 degrees C to 29.5 +/- 0.6 degrees C; P less than 0.001). The majority of patients reported improvement in pain, and two thirds of 12 superficial ulcers healed in 6 weeks. These results show that PGE1, improves digital perfusion for several weeks in patients with severe arterial ischaemia.