Lumbar cerebrospinal fluid (CSF) from 28 non-neoplastic hydrocephalic children was studied for total protein and electrophoretic protein patterns. These were classified as normal, degenerative, transudative and gamma-globulinic according to Laterre. We found higher total CSF protein mean values than in normal cases with the same age and abnormal electrophoretic patterns in 72% of the cases, of which degenerative was the most common (54%). Gamma-globulinic and transudative patterns were found in 11% and 7% of the cases, respectively. Several factors which may explain the increase in the total CSF protein in infantile hydrocephalus are described: low age, ventricular block in the noncommunicating hydrocephalus, and probable passage of tissue proteins to the CSF from the damaged brain. The predominance of degenerative patterns may be explained by the enrichment of the CSF in tissue proteins resulting from the white matter damage provoked by the abnormal conditions of production, flow and absorption of the CSF in hydrocephalus. Ventricular CSF was studied in four cases, and the results obtained are in agreement with the above-mentioned findings.