tests so that those in whom 5 consecutive measurements showed a difference of more than 3 mmHg were excluded. Measurements in 62 of 94 eyes showed a variation of 3 mmHg or less, and these were considered suitable for the definitive studies. All preparations were administered by a third party to ensure double-blindedness on the part of subject and investigator, and were instilled into the left eye. Intraocular pressure' 3 and radial pulse rate over 1 minute after 5 minutes at rest (sitting) were measured before and at 30, 60, and 90 minutes after drug instillation. Three recordings of intraocular pressure in each eye were taken on each occasion and the means recorded.Two studies were carried out, the first comparing timolol 0 25 and 0 5% with normal saline, and the second pindolol 1%, timolol 0-25%, and normal saline. In each study 12 subjects were studied, no subjects taking part in more than 1 study. They attended on 3 occasions at least 1 week apart for instillation of 1 drop into the conjunctival sac (a) timolol 0.25%, 0.5%, or saline 0. 9%, or (b) pindolol 1 %, timolol 0-25 %, or saline 09 %, given in a balanced design based on 4 Latin squares.