Nuclear and cytoplasmic virus RNAs, synthesized in cells infected with herpes simplex virus type 2 at early and late times post-infection, and in the continuous presence of the protein synthesis inhibitor cycloheximide (immediate early), have been analyzed by blot hybridization to virus DNA fragments generated by Bam HI and Eco RI restriction endonucleases. Polyadenylated immediate early mRNAs were separated on denaturing gels containing CH3HgOH giving three virus-specific mRNA bands of estimated sizes 4.7, 3.4 and 1.75 kb, and these have been mapped to five discrete regions of the genome. The polypeptides produced by in vitro translation of the HSV-2 immediate early mRNA's have been identified. Orientations of immediate early mRNA's on the virus genome have been determined by mapping cDNAs complementary to the 3'termini of the mRNAs.