For determination of the gene loci for virulence and tropism of herpes simplex virus 2 (HSV-2) intertypic recombinants of HSV-1 strain HFEM and HSV-2 strain 3345 were screened for their pathogenicity in the tree shrew. HSV-1 strain HFEM is not pathogenic in the tree shrew and can be recovered as a latent virus only from the spleen of the animals; but HSV-2 strain 3345, the other parental virus of the recombinants, was found to be virulent for the tree shrew and colonized the ganglia of latently infected animals. No clinical pictures were observed when the animals were inoculated with HSV recombinants RS1(3), RB2(3), RB2(8), RB2(9), RB2(10), RB5(2), RB7(3), and RB7(7). It was found, however, that HSV recombinant RB5(0) is pathogenic for the tree show. Studies of the state of viral latency in the animals infected with these recombinants revealed that only HSV recombinant RB5(0) was able to persist as latent virus in the spleen of latently infected animals. The genome of recombinant HSV-RB5(0) contains DNA sequences of HSV-2 strain 3345 with two interruptions at 0.22-0.33 and 0.54-0.59 viral map units. In these regions of HSV-RB5(0), DNA sequences of HSV-strain HFEM at 0.26-0.33 and about 0.57-0.58 viral map units, respectively, had been recombined. The results obtained in this study indicate that the recombinant HSV-RB5(0) acquired the virulent phenotype (v+) from parental virus HSV-2 strain 3345 but lost the phenotype for colonizing the ganglia (g+). Furthermore, it acquired the phenotype of parental virus HSV-1 strain HFEM for persisting in a latent state only in the spleen (s+ and g-) of the latently infected animals.