The properties of three herpes simplex viruses isolated in Yugoslavia were studied. The first, a virus isolated from a recurrent herpetic eruption of the thigh, antigenically most closely resembled a laboratory variant and was not typical of human genital isolates. The second was isolated directly from a cervix free of active herpetic infection. It differed from previously isolated type 2 strains in its ability to cause cell fusion and to induce formation of polykaryocytes in tissue culture. In neutralization tests it behaved as a type 2 virus, but it is not identical to isolates from the United States. The third virus, isolated from a recurrent herpetic lesion of the lip of the previous patient, is antigenically a type 1 virus. The possible significance of these findings in providing an explanation for the variability in the biologic properties of herpes simplex viruses was considered.