Seven cases of Pneumocystis carinii pneumonia (PCP) (two in 1988, three in 1989, one in 1990 and one in 1991) have been observed in a group of 241 heart transplant recipients transplanted in Pavia, Italy, from November 1985 through December 1991. Median time to onset of symptoms was 100 days after transplantation (range 59-333 days). Diagnosis was achieved in all patients by cytological examination of bronchoalveolar lavage (BAL) fluid and/or transbronchial biopsy. Clinical and roentgenographic features were remarkably similar in all PCP-affected heart transplant recipients. A dry, persistent hacking cough associated with dyspnoea was consistently observed. Fever ranged from 37.6 to 39.4 degrees C, median leukocyte count and median arterial oxygen saturation (SaO2) values were 7,300/mm3 (range 3,000-16,000/mm3) and 61% (range 49.3-93%), respectively. Median CD4+ count at the onset of symptoms was 211/mm3 (range 28-739/mm3). The only patient experiencing a recurrence of PCP had a CD4+ cell count of 28/mm3 at the end of treatment with trimethoprim-sulfamethoxazole (TMP-SMX). In all patients human cytomegalovirus was isolated from BAL fluids; however, treatment with TMP-SMX alone (20 mg/kg/day of TMP) was consistently followed by a complete recovery.