The intra- and inter-observer variability of Goldmann applanation tonometry was studied in 8 hospital tonometrists, 4 of whom received brief revision training in tonometer use. Intraocular pressure (IOP) measurements were obtained from 16 glaucoma patients. Over a series of four readings taken from individual eyes, intraocular pressure did not significantly vary. However, a decline in IOP was observed when a second tonometrist obtained a further series of four readings from a previously measured eye. Mean pressures recorded by tonometrists who had received revision training were greater than those obtained by the untrained observers though this could be accounted for by two highly experienced individuals in the untrained group who tended to record low pressures. Comparisons of average readings obtained by two observers on the same eye showed that approximately one-quarter of measurements differed by 2 or more mmHg and approximately one-fifth by 3 or more mmHg.