Sympathetic dysfunction and skin microvascular arteriovenous shunting with insufficient nutritive perfusion and tissue hypoxia have been reported in patients with erythromelalgia. The objective of this study was to determine whether iloprost, a synthetic prostacyclin analogue--primarily a vasodilator and inhibitor of platelet activation--improves symptoms and sympathetic function in patients with erythromelalgia. Erythromelalgia is a rare condition, but we managed to collect 12 primary cases for a double-blind, randomized, parallel-group pilot trial evaluating the effect of iloprost (n = 8) and placebo (n = 4). The treatment effect was determined by the need for cooling of affected skin and by vasoconstrictor tests following Valsalva's manoeuvre and contralateral cooling. The results show a significant reduction in symptoms (p < 0.05) and sympathetic dysfunction (p < 0.05) in the iloprost group. Further studies with oral prostacyclins or analogues are suggested.