In just-weaned piglets (n = 30, 3-4 weeks) diarrhoea (100%) and vomiting (66%) were provoked by inoculation with transmissible gastroenteritis virus and enterotoxigenic E. coli strains (O149: K91: K88ac; LT, STa and STb enterotoxin positive). This combined infection resulted in a mortality of 71% within 7 days. During this period animals revealed a decrease in body weight, in arterial pressure, in leukocyte count, in plasma pH and in plasma lactic acid concentrations, and an increase in heart rate and in total plasma protein concentration. In shocked and expiring piglets an increase in haematocrit and a decrease in base excess and actual bicarbonate were observed. Chlorpromazine, administered intramuscularly on 3 successive days following the dual infection in 8 K88ac susceptible pigs, in a dosage of 2 and 1.5 mg/kg.24 h, somewhat retarded the appearance of severe diarrhoea and suppressed vomiting. These beneficial effects, however, did not result in an increased survival.