Central nervous system effects, such as mental confusion and hallucinations, have been reported with both cimetidine and ranitidine. Elderly patients with renal or hepatic dysfunction are more susceptible to these adverse reactions. We report two cases of reversible mental confusion in elderly patients with mild renal insufficiency following intravenous famotidine therapy, possibly explained by an increased permeability of the blood-brain barrier in patients with decreased renal function.