Patient characteristics and pre-hospital drug consumption have been studied in 506 consecutive patients acutely admitted to a department of medicine. Women were older (median 69 years) than men (median 63 years) and weighed less (mean 60 vs. 74 kg). Serum creatinine values were above the normal limits in 110 patients (22%). Forty-eight per cent of men and 26% of women were smokers. Heavy alcohol intake was found in 12% of men and 4% of women. It is concluded that a typical patient group shows much greater variations in age, weight, renal function, smoking and drinking habits--factors all known to influence the results of drug treatment--than is generally taken into account when routine drugs are prescribed.