When a patient with acute drug intoxication is brought to our hospital, the pharmacist must immediately collect pertinent information regarding the causative agents involved, present the collected data and propose therapeutic methods to the doctors and nurses based on the basis of their earlier experience. For the life-saving treatment of a 99-year-old woman who happened to swallow a large amount of diphenhyramine ointment, we proposed gastric lavage and time-lapse measurement of the diphen- hyramine concentration in the blood. The results of this therapy showed a clinical improvement with a drop in the concentration of diphenhyramine in the blood. The conduct of gastric lavage and the clinical determination of diphenhyramine concentration in the blood were found useful in this case.