BACKGROUND: There is evidence that measles virus infection in early life may predispose to Crohn's disease. AIMS: To examine using serological methods a potential association between measles virus infection in early life and predisposition to Crohn's disease. SUBJECTS: Forty five patients with Crohn's disease and forty five healthy controls were studied prospectively. METHODS: Clinical data were recorded and serum was analysed for measles virus, cytomegalovirus (CMV), adenovirus and herpes simplex virus (HSV) antibody titres by a complement fixation test (CFT), and for measles virus IgM by enzyme linked immunosorbent assay (ELISA). RESULTS: Reciprocal CFT titres for measles virus were lower in patients with Crohn's disease compared with controls (p < 0.05); there was no significant difference in titres for other viruses. None of the subjects studied had a level of measles virus IgM suggestive of acute infection, and there was no significant difference in measles virus IgM levels between patients and controls. The measles virus CFT titres and IgM levels in the patients with Crohn's disease did not correlate with any of the clinical features recorded. CONCLUSION: This study does not provide supportive evidence for a role for measles virus in the aetiology of Crohn's disease.