Tonography was performed on 36 eyes of 15 normal and 3 primary open angle glaucoma patients using pneumatonography and classical Schiotz tonography. The average values of the coefficient of outflow facility (C) for the whole sample were virtually identical with both methods. However, both intersubject and interobserver variability were significantly higher with penumatonography. Although both methods provide comparable aggregate estimates of aqueous outflow facility, we think that Schiotz tonography is more reliable than pneumatonography because of the greater mechanical stability of the Schiotz instrument on the eye. On the other hand, pneumatonography offers the advantage of a shorter test period (2 min instead of 4).