The function of the choroid plexus is being examined in experimentally induced hydrocephalus in cats. The cerebral ventricles of these animals were perfused in order to measure CSF formation and glucose transport from blood to the perfusion fluid. The transport of glucose as well as CSF production were decreased by 32% and 46% respectively. The effect of the hydrocephalic process on choroid plexus blood flow was also examined in these same animals. The results indicate that total weight of the choroid pelxus of both normal and hydrocephalic cats are similar. There is however a significant difference in choroidal blood flow between these two groups of cats when measured with radiolabeled microspheres. Choroidal blood flow of hydrocephalic cats is reduced by 56% from a normal value of 342 ml/min/100 gm. Corresponding white matter, grey matter and cortical blood flows of hydrocephalic and normal cats did not significantly differ from each other.