A number of patients receiving continuous intravenous infusions of hyperalimentation solutions require cimetidine (CT) for treatment of gastric hypersecretory conditions. Four patients were selected to receive a CT-hyperalimentation mixture and serial blood sampling for CT concentrations. Rates of infusion of CT ranged from 38 to 56.3 mg/hr. Average serum concentrations (C88) of CT at steady state ranged from 0.6 to 1.0 microgram/ml. This concentration range is near levels reported in patients receiving long-term oral CT and is lower than levels reported to be associated with central nervous system toxicity. No evidence of renal toxicity was noted. Pharmacokinetic parameters were comparable to previous reports in the literature. This initial investigation reveals that continuous intravenous infusion of CT in hyperalimentation solutions appears to be a safe mode of drug administration. More definitive studies are needed to assess efficacy.