To induce diarrhoea and hypovolaemia, newly-weaned conventionally bred piglets (3- to 4-weeks-old), were either given secretagogues or were inoculated with enterotoxigenic Escherichia coli (ETEC). Choleratoxin (n = 2), E. coli heat-labile enterotoxin (n = 2) or castor oil (n = 2) were given intragastrically or piglets were intraperitoneally injected with DL 5-hydroxytryptophan (n = 3). These substances induced a transient diarrhoea without clinical symptoms of dehydration. Therefore, a combination of castor oil and DL 5-hydroxytryptophan was given two times a day during 3 consecutive days to 3 piglets. Although diarrhoea lasted for 5 days, still no hypovolaemia occurred. Probably the secretagogues have to be given continuously to mimic the continuous release of enterotoxins during secretory colibacillary diarrhoea. It was, therefore, tried to reproduce colibacillosis in the just-weaned piglets. Animals were inoculated with K88ac fimbriae producing ETEC strains (O149:K91:K88ac; LT, STa and STb positive) (n = 7), or pretreated with chloramphenicol followed by the ETEC inoculation (n = 8), or pretreated with the antibiotic, inoculated with an enteropathogenic coronavirus, transmissible gastroenteritis virus (TGEV), and subsequently inoculated with ETEC (n = 18). Only the last procedure induced a reproducible diarrhoea (93%) and dehydration resulting in a mortality of 80%. It was concluded that the latter experimental procedure could be used to study diarrhoea and hypovolaemia in newly-weaned piglets and to evaluate the effect of potentially antisecretory drugs on postweaning diarrhoea in piglets.