SINCE the introduction of nitrofurantoin (NF) in the treatment of urinary tract infections, in 1953, some 35 cases have been reported in which this drug has, in the recommended doses, caused peripheral polyneuropathy, occasionally resulting in irreversible paralysis.1-20As nitrofurantoin is mainly excreted through the kidney, abnormally high plasma drug levels resulting from impaired renal function might be considered a causative factor in the production of polyneuropathy. Thus Loughridge10reported that in a patient suffering from nitrofurantoin polyneuropathy and renal insufficiency, plasma drug levels were as high as 6.5μg/ml. She also found raised plasma nitrofurantoin levels in 13 patients with various degrees of renal impairment, who were similarly treated with daily doses of 300 mg of the drug. On the other hand, plasma nitrofurantoin levels in subjects with normal renal functions were found to have a mean value of 1.8μg/ml10and 2.23μg/ml.22 The aim of the