CL115,347 (Cyanamid International) is a stable transdermally absorbed prostaglandin E2 analogue said to have an antiplatelet vasodilatory effect. In a trial of this drug in Raynaud's phenomenon 15 patients were given 1 mg CL115,347/day transdermally for 6 weeks and 14 were given a placebo. The treated group had fewer and shorter spasm attacks and better healing of ulcers as assessed on a visual analogue scale. Blood supply as measured by cold challenge plethysmography ('Medimatic SP2') was also improved by CL115,347, as were hand temperatures. The treated group also had a significant rise in platelet count, but initial decreases in platelet aggregation were not maintained up to the end of the study.