In a retrospective study, we examined the association between cytomegalovirus (CMV) infection and non-neutropenic fever immediately following autologous peripheral blood stem cell transplantation for a variety of haematological malignancies and solid tumours. Sixty non-neutropenic febrile episodes (41 in CMV-seropositive and 19 in CMV-seronegative patients) were evaluated. CMV reactivation, documented by CMV antigenaemia, was detected in 16 out of 41 (39%) seropositive patients compared with 0 out of 19 seronegative patients. In 12 of these 16 patients, CMV infection was considered the sole cause of fever. Thirteen patients had maximum antigenaemia levels > 5 cells/slide. Specific antiviral treatment led to the resolution of the fever in all, but two, patients, who developed fatal CMV pneumonia. Patients with multiple myeloma and lymphoma, possibly owing to a combination of disease-related characteristics and prior immunosuppressive treatment, had high rates of CMV reactivation and may require more frequent diagnostic evaluation and prompt therapeutic intervention.