A repetitive original DNA sequence, TGR1E, was cloned and sequenced, then used to develop a polymerase chain reaction (PCR) test for detecting Toxoplasma gondii. Preliminary studies were performed using purified T. gondii DNA or a lysate of purified T. gondii cells [7], with or without a leukocyte lysate. A negative correlation was evidenced between sensitivity of the test and the amount of cellular debris contaminating the DNA to be amplified. Nevertheless, the method was tested on 100 clinical specimens subjected to lysis using the same method. Among the 88 specimens from AIDS patients, four were positive by conventional diagnostic tests and by PCR. Among the 12 specimens tested as part of evaluations for the prevention of congenital toxoplasmosis, PCR failed to detect the positive results yielded by conventional tests on two amniotic fluid specimens. No false positive result was seen with the PCR method.