The incidence and clinical importance of infectious gastroenteritis was studied in 67 consecutive relapses of inflammatory bowel disease (IBD). A stool culture was done in every case before starting treatment. Stool culture was positive in 6 relapses (8.9%): Four were exacerbations of ulcerative colitis and two of Crohn's disease (8.8% in ulcerative colitis vs 9% in Crohn's disease; NS). The microorganisms isolated were Campylobacter jejuni in three cases, Salmonella enteritidis in two and Staphylococcus aureus in one case. There were not clinical differences between patients with positive and negative stool culture. Treated with antibiotics, stool cultures became negative in all of them but only in three the disease was controlled. The other three had to be treated with corticosteroids to achieve remission. We conclude that stool culture should be practised in all relapses of IBD and in case of positivity, antibiotic therapy should be started. With this approach the use of corticosteroids can be avoided in some patients.