Analysis of the proteins of capripoxvirus (KS-1) revealed a 32kd protein that is one of the major structural proteins of the virus and is localised in the virus envelope. Monospecific serum prepared against the 32kd envelope protein neutralised the virus indicating that this protein contains neutralising epitopes. Lymphocyte proliferation studies, using the 32kd protein and peripheral blood mononuclear cells from capripoxvirus (KS-i) vaccinated sheep, showed that this protein strongly induced cellmediated immune responses. The 32kd protein is capripoxvirus specific and induced antibodies in early stages of capripoxvirus infections. Immunoblot analysis of antibody responses against this protein has provided a basis for the differential diagnosis of capripoxvirus and orf virus infections. The 32kd protein bound to the surface of cultured lamb testis cells. The binding of the 32kd protein was completely inhibited by prior incubation of cells with purified capripoxvirus (KS-1) but not by bovine serum albumin. Trypsin treatment of capripoxvirus (KS-1) degraded the majority of the 32kd protein with a minimal effect on a few other virus proteins. Trypsin removed an external 10kd fragment from the 32kd protein, leaving a 22kd fragment associated with the virus. In addition, the trypsin treatment reduced the virus infectivity by at least ten fold, suggesting that the cell surface binding domain of the 32kd protein is located within the external 10kd fragment. The monospecific serum to the 32kd protein had no effect of the infectivity titre of the trypsin treated virus further supporting the concept that the external 10kd fragment of the 32kd protein is involved in binding of the virus particle to the cell surface. A degenerate oligonucleotide probe, based on an internal amino acid sequence obtained from V8 protease cleavage products of the 32kd protein, was used to identify the gene encoding the 32kd protein. The gene encoding the 32kd protein was identified within the 2.8kb HindI1l Q1 fragment of the capripoxvirus (KS-1) genome. The nucleotide sequence analysis of the Hindu Q1 fragment revealed five open reading frames (Q11L, Q12R, Q13L, Q14R and Q15L), one of these open reading frames, Q13L, is capable of encoding a 30.6kd protein and contains the complete internal amino acid sequence obtained from the V8 protease cleavage products of the 32kd protein, indicating that the Q13L encodes the 32kd envelope protein of capripoxvirus (KS-1). The deduced amino acid sequence of the Q13L shows a 34.1% identity and 61.3% similarity with that of H3L open reading frame of vaccinia virus.