Children with defective yeast opsonisation are more likely to have chronic diarrhoea and this can be halted by infusion of fresh plasma. It is not known whether these children have diarrhoea because of persistence of known stool pathogens, development of an enteropathy or some other mechanism. This study seeks to explore the association of stool pathogens and small intestinal enteropathy with defects in opsonisation. Thirty-two children (10F;22H, aged 3 mo to 7 yr) with chronic diarrhoea were investigated for yeast opsonisation, stool pathogens and an enteropathy. Thirteen (3F:10M) had severe opsonisation defects, of whom two had stool pathogens and six had an enteropathy, which appeared to account for the idarrhoea; however in six stool bacteriology an small bowel biopsy were normal and no other diagnosis was reached. Conversely, in those with normal opsonisation who had a normal small bowel biopsy and were free of stool pathogens a diagnosis was reached in all but one case. This included toddler's diarrhoea, response to food elimination. Severe atopy, IgE subclass deficiency and small intestinal bacterial overgrowth. The chronic diarrhoea found in children with defective yeast opsonisation often occurs independently of the presence of stool pathogens or an enteropathy.1. Candy DCA et al. ARch Dis Chil 1980; 55 : 189.