Herpes simplex viral DNA was detected in biopsy specimens obtained from four patients with Kaposi's varicelliform eruption using an in situ hybridization technique with biotinylated complementary DNA probes. Herpes simplex viral DNA was consistently found almost exclusively in the nuclei of giant cells and balloon cells in vesicles during day 2, 5 and 7 of the disease. In the nuclei, the viral DNA staining pattern was granular or agglomerate. No positive staining was observed in the cytoplasm.