Thirty subjects with clinically diagnosed toxoplasmosis retinal lesions, and 30 control subjects matched for age, sex, and race, were evaluated for the presence of IgG antitoxoplasmosis antibodies by enzyme-linked immunosorbent assay (ELISA) methodology. Positive titer was found in 56% of subjects and 20% of controls. Positivity of titer was not correlated to location of lesion, laterality, presence of satellites, sex, or race. Increasing age in both subjects and controls was weakly correlated to positive titer. Study results indicate that a relative overdiagnosis of toxoplasmosis occurs if positive antibody titer is accepted as criteria for positive diagnosis. Currently employed criteria based on physical findings appear to be of little value in predicting positive titer.