We have determined the DNA sequence of the long repeat region (RL) in the genome of herpes simplex virus type 1 (HSV-1) strain 17, as 9215 bp of composition 71.6% G + C. In addition, the sequences of parts of the long unique region (UL) adjacent to the terminal (TRL) and internal (IRL) copies of RL were determined (2611 and 3836 bp, respectively). Gene organization in these regions of UL was deduced from the sequences and other available data. It was proposed that the region of UL sequenced, adjacent to TRL, contains three complete genes, none with significant previous characterization, and that the region of UL adjacent to IRL also contains three genes, one encoding the immediate early protein IE63. The RL sequence contains one well characterized gene, for the protein IE110, whose organization we have described previously. Between the downstream end of the IE110 gene and UL there is a 3500 bp segment of RL in which we did not find convincing protein-coding sequences, and which thus remains of obscure functionality. Upstream of the IE110 gene is a region previously proposed by others to contain a gene. However, our sequence data are not compatible with their interpretation. We do consider it possible that the region is protein-coding, but regard gene organization here as still unresolved.