In spots of amniotic fluid from the time of delivery placental alkaline phosphatase was detected reliably by the azocopulation reaction after inactivation of the thermolabile fraction. Evidence was positive in all 82 examined samples collected during delivery. A positive test was obtained already during the 16th week of gestation, while in the first trimester the result of the reaction was uncertain. Detection in the spots is better than in the extract from the spot and can be made event after two months. On the other hand, a test made on a slide makes also morphological examination possible. As regards evidence of pregnancy origin of the spots, the test is specific.