The hamster papovavirus (HaPV) is a polyoma virus with a restricted tumor spectrum. It is actively replicated in hair follicle tumors arising spontaneously in young Syrian hamsters. It can also induce lymphomas and leukemias in newborn hamsters. The complete nucleotide sequence of a cloned HaPV has been established recently. This report presents a comparison of this sequence with other polyomavirus genomes (polyoma, SV40, BKV, LPV) by matrix dot analysis and electron microscopy heteroduplex mapping. The results demonstrate a close relationship between the HaPV and the murine polyoma virus and designate the LPV as the closest relative among the primate polyomaviruses.