A field survey conducted in 94 ophthalmologists' offices in our immediate area assessed the accuracy of tonometers in daily use. One hundred eighty-five instruments were examined: 127 were slit lamp mounted, 48 were hand held, and 10 were noncontact devices. Nineteen percent of applanation tonometers were outside the manufacturers' specifications (1 mm Hg of the calibration) and 4.5% were more than 2 mm Hg in error. The error was constant across the scale. Hand-held applanators were less accurate than those on slit lamps (P less than .02); the latter demonstrated an association between accuracy and age (P less than .05) and heavier use (P less than .01). Annual recalibration was performed in 86% of instruments. Those practitioners who themselves performed the calibration had the most accurate instruments. Less than 15% knew how to perform the calibration check.