Serology testing is an appropriate method for the detection of slaughter animals infected with Toxoplasma, which remain one of the main reservoirs of this parasite in the environment. Competitive ELISA (cELISA) in indirect modification was worked out and optimized for detecting antibodies to Toxoplasma gondii in pigs and cattle. Preliminary validation process showed that the sensitivity and specificity of cELISA obtained in pigs was better than in cattle (88.1% and 94.5% vs. 76.9% and 93.4%, respectively). Sera of 861 pigs and 865 cattle were examined with newly worked out cELISA test and modified agglutination test (MAT) (Toxo-Screen DA, bioMérieux, France). In the total of 1,726 examined animal sera, seropositive results were obtained in 15.0% by cELISA (15.4% in pigs and 14.6% in catttle), and in 13.6% by MAT (14.3% in pigs and 12.8% in cattle). Significant differences in percentages of positive results among populations of the studied animals from various areas of Poland were noted. Obtained results showed the usefulness of cELISA for examining sera of slaughter animals (especially pigs). The considerable rates of infection of slaughter animals with T. gondii in the area of research indicate a potential threat to human health.