Proteins of the piroplasms of Theileria sergenti, T. buffeli and T. orientalis were analysed by two-dimensional polyacrylamide gel electrophoresis. Protein spot patterns of T. buffeli and T. orientalis were identical except for a few minor proteins, whereas spot patterns of two T. sergenti stocks were differentiated from those of T. buffeli and T. orientalis by a characteristic set of proteins including a major protein of molecular weight 33–34 kDa. This result indicates that Japanese T. sergenti can be phenotypically distinguishable from European and Australia Theileria species; T. orientalis and T. buffeli.
