Twenty-six blood samples were used in this study. Six of thero were collected from six experimentally infected calves with T.anmilata strain while twenty blood samples were collected from asymptomatic cattle with theilerosis at four endemic provinces in Egypt. All samples were subje to microscopic examination, fluorescent antibody test (IFA), and polymerase chain reaction (PCR). The carrier animals were detected in 11 out of 20 blood samples microscopically (55%) and in 10 of 20 by using IFA (50%) whereas PCR revealed that 16 samples were considered to be carrier positive(80%). Two sets of primers were used in PCR technique. A primer set A, derived from the sequence of the small subunit rRNA (SSURNA) of Theileria species, amplified 1.098 bp product for detection of Theileria spp. DNA. While a primer set B, deduced from the gene encoding the 30 KDa major merozoit surface antigen of T. annulata was successfully amplified 721 bp product. The PCR technique provides a useful diagnostic tool for detection of T. annulata carrier cattle even at low parasitaemia levels.