Toxoplasmosis seroprevalence varies considerably between countries. We studied the seoprevalence of Toxoplasma gondii IgG antibodies in a national sample of the Israeli population; 2794 sera were tested. The highest age-adjusted seroprevalence rate was in Arabs (non-Bedouins) (60·4%), significantly higher compared to the rate in Jews (19·9%) and Bedouins (27·5%) (P < 0·01). There were no significant gender differences. Seropositivity increased with age in all population groups. For Jews, seropositivity was associated with place of birth and socioeconomic status. A finding of low seroprevalence rate in Bedouins despite their poor living conditions and close contact with livestock is surprising, and might be attributed to the dry and hot climate conditions in their area of residence. In women of reproductive age the seroprevalence was 15·1% in Jews, 25·4% in Bedouins and 72·3% in Arabs (non-Bedouins). Thus, the majority of pregnant women are susceptible to primary infection with T. gondii, and the risk for congenital toxoplasmosis remains high.