We performed a clinical evaluation on a prototype version of the Tono-Pen hand-held tonometer. A masked, randomized design was used to compare the instrument with the Goldmann tonometer. We tested 270 eyes. For pressures of 6 to 24 mm Hg, the Tono-Pen tonometer measured, on average, 1.7 mm Hg higher than the Goldmann tonometer. This difference was statistically significant (P less than .0001). In the range above 24 mm Hg, no statistically significant difference was found in the pressures measured with the two instruments. Measurements made with the Tono-Pen were sufficiently close to those made with the Goldmann tonometer to be considered clinically accurate.