Molluscum contagiosum virus was purified by two methods involving differential centrifugation; treatment with ribonuclease and sucrose density gradient centrifugation. When the final gradient centrifugation was preceded by two consecutive centrifugations through 36% sucrose, the percentage of DNA in the purified virus particles was reduced. The purified virus was similar to purified vaccinia virus in DNA content, in the absence of detectable RNA and in sedimentation characteristics. Treatment of secondary mouse embryo monolayers with purified molluscum virus caused a reduction in the number of viable cells and in the amount of DNA/culture but had little effect on the amounts of RNA and protein/culture. The depression in the rate of DNA synthesis was maximal at about 24 to 36 hr after infection.