Toxoplasmosis is caused by an obligate intracellular protozoan parasit
e, Toxoplasma gondii. Most of the toxoplasma infections are asymptomat
ic or benign, but may cause severe or fatal consequences in immunodefi
cient patients, transplant recipients, and in the fetus. Transmission
may occur by eating uncooked meat, contaminated vegetables, blood tran
sfusion, organ transplantation, and across the placenta from the mothe
r to the fetus. Antibodies to T. gondii may persist in the serum at hi
gh titers for years. We screened 784 Saudi blood donors using indirect
hemagglutination test and 294 (37.5%) were found to be seropositive a
t different titers. The highest rate of seropositivity was found in th
e age group 21 to 30 years in males, and after 40 years of age, the pr
esence of antibodies declined. Among females, the higher rate of serop
ositivity in the age group 18 to 20 years should be confirmed by furth
er studies.