Object. Besides mechanical damage done by the enlarging ventricles, biochemical impairment in the periventricular tissue represents an important factor resulting from or contributing to the pathogenesis of hydrocephalus. In this study the changes in periventricular region total sialic acid levels in the early stage of experimentally induced hydrocephalus were evaluated. Methods. Hydrocephalus was induced in 3-week-old rat pups by kaolin injection into the cisterna magna. Ten days after hydrocephalus induction rats were sacrificed and total sialic acid levels in the periventricular area were determined by the thiobarbituric acid method. Conclusion. Sialic acid, a vital component of brain gangliosides, which play an essential role in the transmission and storage of information in the brain, was found to be significantly decreased in the periventricular area of hydrocephalic infantile rats.