Single or multiple lung nodules or masses were noted at chest radiography in 25 (9.7%) of 257 patients after cardiac transplantation. Two episodes occurred in each of three patients, for a total of 28 (10.9%) episodes in the 257 patients within the first 18 months after transplantation (transplantation performed between July 1987 and December 1990). Bronchoscopy, percutaneous needle biopsy, and open lung biopsy were performed as clinically warranted to establish a diagnosis. Infection was found in 21 instances (8.2%) in 18 patients. The most frequent pathogens were Aspergillus (n = 9 [3.5%]) and Nocardia (n = 7 [2.7%]). Aspergillus was hospital acquired in eight (89%) of nine patients and had a right-sided predominance (20 [74%] of 27 lesions). The nodules or masses appeared a median of 2 months after transplantation for Aspergillus (range, 0.5-12 months) and 5 months for Nocardia (range, 1-10 months). B cell lymphoma manifested as numerous nodules in two patients (0.8%). Although a variety of causes were found for post-cardiac transplantation nodules or masses, the majority (75%) were infectious.