An antigenically distinct adenovirus is described which was isolated in March 1972 from the urine of a 17-year-old Caucasian male who was experiencing fever after receiving a kidney transplant from a cadaver in February. The adenovirus could not be isolated in April from a pharyngeal swab which yielded cytomegalovirus. Complement-fixation, hemagglutination-inhibition, and/or serum-neutralization tests on sequential serum specimens from the patient confirmed that the adenovirus infection occurred during March and showed that infections with cytomegalovirus and respiratory syncytial virus also occurred during late March and April. The patient's persistent fever, for which other causes could not be found, may have been associated with one or more of these infections. Upper respiratory symptoms and lung involvement were not found during this period. Mild liver dysfunction during this time could not be clearly related to adenovirus infection because of the presence of multiple other causes. The adenovirus may have been latent in the donor kidney and become active in the new host as a consequence of immunological impairment. The adenovirus, purified by terminal dilution and plaque procedures, has antigenic, morphological, biophysical, host susceptibility, and hemagglutinating properties characteristic of adenovirus group IA. Buoyant densities in CsCl are 1.340 g/ml for the virion, 1.304 g/ml for the group CF antigen (hexon), 1.295 g/ml for the major soluble complete hemagglutinin (dodecon), and 1.206 g/ml for the minor soluble complete hemagglutinin (tentatively, fiber dimer). The virus does not cross-react in reciprocal hemagglutination-inhibition and serum-neutralization tests with antisera to adenovirus types 1 to 33. We propose this virus as candidate adenovirus type 34 (Compton).