South African Angora goats (Capra hircus) are susceptible to cold stress, due to the inability of the adrenal cortex to produce sufficient levels of cortisol. Two CYP17 isoforms were identified, cloned and characterized in this study. Sequence analysis revealed three amino acid differences between the two CYP17 isoforms, which resulted in a significant difference in 17,20 lyase activity of the expressed enzymes in both the presence and absence of cytochrome b(5). Furthermore, cotransfections with 3 beta HSD revealed that one CYP17 isoform strongly favours the Delta(5) steroid pathway. Our data implicates CYP17 as the primary cause of the observed hypoadrenocorticoidism in the South African Angora goat.