The authors investigated the effect on pHof the aqueous humourin man(collected before surgery of senile cataract, where the pHof the aqueous humour was within the range of 6.80-7.46 (7.11 ± 0.11), after administration of antiglaucomatic drugs with a different concentration and pH (0.005% Xalatan - pH 6.43, 0.5% Timoptol - pH 6.80, 1% Pilocarpine - pH 5.87, 2% Trusopt -pH 5.33) under conditions in vitro. All mentioned antiglaucomatic drugs immediately reduced the pH of the aqueous humourtowards acid values in the followingorder: Trusopt - Xalatan - Pilocarpine - Timoptol. pH changes of aqueous humour after addition of Timoptol, Xalatan, Pilocarpine have the same course in time, and shift to alkaline pH values. The pH of aqueous humourafter addition of Trusopt reachedonly during the 240th minute levels of the control aqueous humour. The pH values after all antiglaucomatic drugs did not change between 240 minutes and 24 hours. As regards the rate of activity andextent of effect in conjunction with the timewhenthe pHof the control aqueous humour was attained the authors recorded the following order: Pilocarpine - Timoptol -Xalatan - Trusopt

        Key words: pH of aqueous humour, effect of antiglaucomatic drugs on aqueous humour of man, course of effect of aqueous humour pH with antiglaucomatics