To evaluate ventriculo-cisternal perfusion as a method for measuring cerebrospinal fluid formation rate, calculated by means of the Heisey et al equation. Method. All experiments were carried out on anesthetized domestic cats fixed in the sphinx position in a stereotaxic frame. Ventriculo-cisternal perfusion was used at an intracranial pressure of -10 cm H2O at different perfusion rates (32.0, 65.5, 125.0, and 252.0 microL/min). Dextran blue was applied as an indicator substance and the concentration of the indicator was measured with a spectrophotometer at a wavelength of 635 nm. Cerebrospinal fluid formation rate was calculated with the equation of Heisey et al. Results. The indicator substance was less diluted at a higher perfusion rate, and the calculated cerebrospinal fluid formation rate was lower. The increase in perfusion rate from 65.5 to 125.0 to 252.0 microL/min increased the concentration of indicator substance from 0.75 to 0.89 to 0.97 mg/mL and decreased calculated cerebrospinal fluid formation rate from 21.8 to 15.4 to 7.8 microL/min. This reduction was linear and an increase in the perfusion rate by 1.0 microL/min decreased the cerebrospinal formation rate by 0.05 microL/min. Conclusion. The calculated cerebrospinal fluid formation rate depends on different perfusion rates. The increase in the perfusion rate diminishes the calculated formation rate. Ventriculo-cisternal perfusion may not be a suitable method to calculate the cerebrospinal fluid formation rate according to the equation of Heisey et al.