Clinical and microbiological data were collected prospectively from 704 patients who underwent bone marrow transplantation (BMT) during an 11-year period (1991-2001), and the first two cases of Campylobacter infection occurring in BMT recipients in the pre-engraftment period were identified. The two cases occurred on days 2 and 3 post-BMT, respectively. Both patients had Campylobacter jejuni enteritis, and one case was complicated by bacteraemia. In both cases the presenting symptoms were indistinguishable from hospital-acquired pre-engraftment diarrhoea, which is commonly caused by Clostridium difficile. Both of the Campylobacter jejuni isolates were resistant to cotrimoxazole and ciprofloxacin. Both patients responded to intravenous meropenem and subsequently had uneventful marrow engraftment.