The AO II non-contact tonometer (NCT) was compared with the Goldmann applanation tonometer (GAT) in 50 patients preoperatively and on the first day after cataract surgery. After pooling the preoperative and postoperative values, the relationship between NCT (y axis) and GAT (x axis) was described by the following regression: y = 1.01x - 0.69, where 1.01 is the slope and -0.69 (in mm Hg) is the y intercept of the regression line. The standard deviation (SD) in relation to the regression line was 2.19 mm Hg (y values). After separating the preoperative (n = 100; pressure range 6-21 mm Hg) and postoperative values (n = 47; pressure range 6-30 mm Hg) the following equations were obtained: preoperatively: y = 0.89x + 0.82 (SD 2.2 mm Hg); postoperatively: y = 1.06x - 1.15 (SD 2.24 mm Hg). Since the postoperative regression line comes close to that required for legal verification, the NCT may - with limitations - also be recommended for measuring IOP after cataract surgery. Both preoperatively and postoperatively, a significantly linear relationship was found between corneal thickness and the difference GAT minus NCT readings. This implies that in normal eyes with thin corneas the NCT tends to underestimate IOP, while in eyes with thick corneas there is a tendency to overestimate IOP. Even slight corneal edema (postoperatively) reduces this effect.