Summary. A prospective study of 62 chemotherapy- induced neutropenic episodes in patients with acute leukaemia was conducted to determine the incidence and causes of abdominal infections, and to assess the diagnostic value of the combined use of ultrasonography (US) and microbiology. Each patient underwent US of liver, gallbladder and complete bowel before chemotherapy, on days 2–4 after the end of chemotherapy and in cases of fever, diarrhoea or abdominal pain. US was combined with a standardized clinical examination and a broad spectrum of microbiological investigations. From January to August 2001, 243 US examinations were performed. The overall incidence of abdominal infectious diseases was 17·7% (11 out of 62, 95% confidence interval (CI): 9–29%). Four patients (6·5%) developed neutropenic enterocolitis; two of them died, two survived. Bowel wall thickening (BWT) > 4 mm in these four patients ranged from 5·8 to 23·6 mm and was detected only in one patient with mucositis. In three other patients (4·8%) Clostridium difficile, and in one patient (1·6%) Campylobacter jejuni, caused enterocolitis without BWT. Cholecystitis was diagnosed in three patients (4·8%) and hepatic candidiasis was strongly suspected in one patient. Abdominal infections caused by gastroenteritis viruses, cytomegalovirus (CMV) or Cryptosporidium were not observed. We conclude that in neutropenic patients with acute leukaemia receiving chemotherapy: (i) BWT is not a feature of chemotherapy-induced mucositis and should therefore be considered as sign of infectious enterocolitis; (ii) viruses, classic bacterial enteric pathogens (Salmonella, Shigella, Yersinia, Campylobacter, Aeromonas, Vibrio subsp., enterohaemorrhagic Escherichia coli) and Cryptosporidium have a very low incidence; and (iii) abdominal infections may be underestimated when US is not used in every patient with abdominal pain.