Four cases of severe peripheral neuropathy directly attributable to nitrofurantoin are reported. The neuropathy was not dose-related and not necessarily associated with abnormal renal function. Recovery was slow, and neither severity nor recovery was related to the total dose of the drug. The pathological changes seen on light microscopy and electron microscopy were those of acute, severe axonal degeneration. It is emphasised that nitrofurantoin is a neurotic drug and should not be prescribed to the elderly not to anyone with impairment of renal function.