The neuropathology of 31 cases of cardiac transplantation is reported. Lesions were found in the central nervous system of 18 cases, and were infectious, vascular, or neoplastic in nature. Fungal meningoencephalitis or abscess formation was found in 5 patients as part of a disseminated fungal infection. Aspergillus was the organism in 3 instances, and Candida or Mucormycesin 1 each. In 10 cases, disseminated microglial nodules were found in the brain in association with intranuclear inclusions suggestive of herpesvirus in the lungs. In two instances, large amphophilic intranuclear inclusions were found in neurons, and an antemortem rise in cytomegalovirus serology titre was demonstrated in two cases. The presence of widespread microglial nodules was interpreted as suggestive of viral encephalitis, with cytomegalovirus as the probable prevailing agent. In 1 case, Toxoplasma organisms were also demonstrated. Vascular lesions were seen in 5 cases, which included thrombotic embolisation in the middle cerebral artery in 1 case and multiple cerebral fat emboli in another. 1 patient had a reticulum-cell sarcoma-microglioma in the cerebellum, associated with a similar neoplastic lesion in one lung eight months after cardiac transplantation.