Restriction endonuclease mapping was used to determine the molecular structure of feline herpesvirus type 1 (FHV-1) strain B 927. FHV-1 DNA purified from infected cells by pulsed field gel electrophoresis was partially restricted with Sau 3A to generate a series of overlapping fragments of 10-20 kb. EMBL 4 DNA was digested with Bam HI and Sal I and viral DNA was inserted into the "stuffer" region. Recombinant phage were selected on E. coli strain Q359. Single and double digestions with the enzymes Eco RI, Bam HI, Sal I, Sst I and Xho I enabled construction of physical maps of the genome. The FHV-1 genome is approximately 126 kbp in length and is composed of a long unique region of 99 kbp and a short region of 27 kbp comprising an unique sequence of 8-9 kbp flanked by inverted repeats of 7-8.5 kbp.