A double-blind placebo-controlled study was carried out in 14 subjects to investigate the effect of naftidrofuryl in the treatment of rest cramp. Naftidrofuryl caused a significant reduction in cramp frequency (median naftidrofuryl = 5; median placebo = 17; P < 0.004) and a significant 34% increase in cramp free days (median naftidrofuryl = 22; median placebo = 14; P < 0.004). Naftidrofuryl is an effective alternative to quinine in the treatment of this painful condition.