Forty-five consecutive adult patients with haematological malignancies were studied prospectively to evaluate cardiac involvement in bone marrow transplantation (BMT). Echocardiography and measurement of systolic time intervals were performed before conditioning with cyclophosphamide (CY) (120 mg kg-1) and total body irradiation (10-12 Gy), and repeated 1 month and 1 year after BMT. The left ventricular (LV) changes at the 1-month study included increases in mass index (85.1 +/- 4.0 g m-2 vs: 76.1 +/- 3.3 g m-2, mean +/- SE; P less than 0.001) and in the pre-ejection period/ejection time ratio (0.46 +/- 0.01 vs. 0.36 +/- 0.01, P less than 0.001), and decreases in fractional shortening (24.9 +/- 1.0% vs. 27.9 +/- 0.8%, P less than 0.01) and in the peak normalized diameter lengthening rate (2.2 +/- 0.1 s-1 vs. 2.6 +/- 0.1 s-1, P less than 0.01). Four patients developed congestive heart failure. Twenty-four patients were alive and relapse-free 1 year after BMT. The LV measurements were then no longer different from the pre-transplant readings. Thus BMT that is preceded by conditioning with CY and total body irradiation results in increased LV mass and impaired systolic and diastolic LV function. These changes are mostly subclinical, and are also reversible if the recipient survives the initial months after transplantation.