Lymphotropic papovavirus (LPV) is a new member of the polyomavirus genus. Its host range in vitro is restricted to transformed cells of B-lymphocyte origin. Here the complete 5270-bp DNA sequence of LPV is presented. The LPV early region can encode a large T and a small t antigen but no middle T antigen and the late region can encode the three structural proteins VP1, VP2, and VP3. Based on sequence conservation of shared proteins LPV is equally related to both mouse polyomavirus (Py) and simian virus 40 (SV40) and represents a new distinct species of the polyomavirus genus. Sequence comparisons of LPV, SV40, and Py point out essential conserved sequence features of the polyomavirus genus more clearly than the comparison of only SV40 and Py. The most conserved proteins are VP1 with 42% and large T antigen with 28% of the amino acids conserved among the three viruses. Although least conserved the noncoding DNA sequences of LPV show significant homologies both to SV40 and Py (origin of viral DNA replication and putative early promoter). A 63-bp tandem repeat at the late side of the replication origin possibly represents a LPV enhancer element.