The genome of a virulent strain (LIS57) of African swine fever virus differs from that of the Vero-cell-adapted strain (BA71V) in several deletions located in the variable regions. The region which contains the most differences is located 8-20 kb from the left end. The DNA sequence of this region was obtained from LIS57 virus DNA and compared with the overlapping sequences of BA71V virus. This comparison revealed that the changes in the variable regions result in differences in the number of genes which belong to the multigene families 360 and 110. Virus isolate LIS57 contains at least 8 genes of the multigene family 360 and 12 genes of the multigene family 110, instead of the 6 and 5 genes, respectively, found in BA71V virus strain. The position of the deletions indicates that new combinations of multigene family members in African swine fever virus DNA may arise by in-frame recombination between homologous genes. These data indicate that the evolution of the multigene families 360 and 110 in African swine fever virus DNA has involved different processes, including gene duplication, divergence of duplicated genes, and gene deletion.