The adrenal cell test for detection of heat-labile enterotoxin-producing Escherichia coli was performed on faecal specimens collected over a period of six months from 648 patients with diarrhoea. The patients came from all parts of Sweden. A total of 72 enterotoxigenic strains were found in 27 patients. Enterotoxigenic strains do not seem to be an important cause of diarrhoea in Sweden, since 70% of the patients with enterotoxin-producing strains had been abroad. Enterotoxigenic enterobacteria were the cause of traveller's diarrhoea in 11% of the patients who had been abroad with a peak incidence in July and August when traveller's diarrhoea was associated with enterotoxigenic strains in 17% of the patients. A simplified method for screening a large number of specimens for enterotoxin production was evaluated and found to be useful.