The gene encoding protein p17, a major structural protein of African swine fever virus, has been mapped and sequenced. Protein p17 was purified from dissociated virus by reverse-phase HPLC and the amino acid sequence of a peptide obtained after digestion of protein p17 with cyanogen bromide was determined by automated Edman degradation. To map the gene encoding protein p17, a mixture of 17-mer oligonucleotides based upon a part of the amino acid sequence was hybridized to cloned African swine fever virus DNA restriction fragments. This allowed the location of the gene in the fragment EcoRI D of the viral genome. The nucleotide sequence of a Sa/l/KpnI fragment revealed an open reading frame designated D117R encoding a protein of 117 amino acids with a deduced molecular mass of about 13,000 Da. A transcriptional analysis revealed that the p17 gene is expressed late in the viral infection cycle.