A review was made of experimental methods available to produce congenital hydrocephalus by teratogenic methods. Radiation, infections, trypan blue, hypervitaminosis A, salicylates and nutritional deficiencies were considered. In the course of prenatal zinc deficiency experiments, congenital hydrocephalus was frequently encountered and histologic sections were made of many representative specimens. Details of the findings are described, among them various types of aqueduct stenosis or obliteration. Although these anomalies suggest that occlusion of the aqueduct is the cause of the enlargement of the ventricular system it was noted that there was also ventricular dilatation caudal to the stenotic point of the aqueduct. Hydrocephalus without aqueductal stenosis has also been observed in experimental animals. It seems possible that some cases of congenital hydrocephalus attributed to aqueductal stenosis are examples of hydrocephalus with secondary block of the aqueduct.