We used the polymerase chain reaction to amplify DNA fragments specific to Toxoplasma gondii. The sensitivity of the technique allowed for the detection of as few as ten cultured T. gondii tachyzoites. We applied the same amplification technique to deparaffinized ocular sections from two cases of ocular toxoplasmosis. Although toxoplasmic cysts could only be seen in one eye by optical microscopy, polymerase chain reaction allowed the identification of the parasite in both cases. Our study indicates the feasibility of a sensitive DNA-based assay to complement pathologic studies of an ocular parasitic disease.