A poxvirus has been isolated from Molluscum Contagiosum lesions. The purified virus particles will replicate in several cell lines but human embryonic kidney cells seem superior to other tried. Since the virus causes no cytopathic effect, the replication is followed by determining incorporation of radioactive thymidine into particles with a specific buoyant density. These virus particles have been isolated and replicated from every Molluscum Contagiosum lesion but are not present in normal skin from the same patient or in similar types of skin lesions. Patients with Molluscum Contagiosum have low levels of antibodies which neutralize this virus. No other population of patients have these neutralizing antibodies.