Four patients with connective tissue disease who had been suffering from severe Raynaud's phenomenon were treated with an intravenous infusion of prostaglandin E1 (PGE1) and its effectiveness was assessed by thermography and a questionnaire approach. PGE1 in a lipid microsphere formulation (lipo-PGE1) produced a significantly greater increase in lesional skin temperature compared with treatment with PGE1 clathrated in alpha-cyclodextrin 12 months previously in the same group of patients. These results were supported by the subjective assessment obtained from the patients by questionnaire.