The purpose of this study was to compare the haemodynamic effects of intra-arterial and intravenous prostaglandin E1 (PGE1) both injected and infused into ischaemic legs. Continuous intra-arterial infusion of PGE1 induced a significantly greater increase in skin temperature and blood flow than did intravenous drip infusion. Furthermore, intra-arterial infusion caused no steal phenomenon in the toe as indicated by skin temperature. On the other hand, toe skin temperature decreased during intravenous drip in 33 per cent of the legs tested. Continuous intravenous infusion also produced a significantly greater increase in toe skin temperature than did brief intravenous drip. In three of ten ulcers healed by continuous intra-arterial infusion, no definitive effect was obtained from continuous intravenous infusion even when it was repeated up to three times before continuous intra-arterial infusion. Intra-arterial injection of PGE1 caused no significant increase in toe skin temperature.