Clinical and laboratory findings of 78 paediatric patients with infections due to enteroinvasive bacteria were analysed. The material included 33 cases of Yersinia enterocolitica, 21 of Campylobacter jejuni, 21 of Salmonella and 2 of Shigella infection, reflecting the current order of frequency ot these enteropathogens in Finnish paediatric population. Diarrhoea was the presenting symptom in 73% of the cases with Yersinia, 90% with Campylobacter and 100% with Salmonella. Conversely, abdominal pain on admission occurred more frequently (p less than 0.01) in patients with Yersinia (68%) than with Campylobacter (38%) or Salmonella (24%). Diarrhoea caused by each of the three enteric bacteria was clinically indistinguishable, with gross blood and mucoid stools occurring in most of the cases. However, faecal leucocytes were more frequently present in diarrhoea due to Y. enterocolitica (87%) and C. jejuni (83%) than Salmonella (36%); p less than 0.025). Diarrhoea due to Y. enterocolitica was typically associated with signs of systemic response, including fever greater than or equal to 39 degrees C, WBC count over 11 X 10(9)/l, and C-reactive protein greater than or equal to 10 mg/l. These criteria may thus be helpful in differentiating Yersinia infections from other cases of exudative diarrhoea in children. The clinical picture of Y. enterocolitica infection probably reflects the more invasive nature of this enteropathogen as compared with C. jejuni or Salmonella.