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Objective To evaluate the effect of topical 2% dorzolamide alone, and in combination with topical 0.5% timolol, on intraocular pressure (IOP) in normal cats. Animals Twenty-four healthy Domestic Short-haired cats. Procedure Baseline values of IOP were established at 7 am, 10 am, 1 pm, 5 pm and 9 pm during pretreatment phase (days 1–2). During treatment phase (days 3–10) cats received 2% dorzolamide HCl q 12 h in group A ( n = 6), q 8 h in group B ( n = 6), and combined with 0.5% timolol maleate q 12 h in group C ( n = 6). Cats in control group D ( n = 6) received artificial tears q 8 h. During treatment phase IOP measurements were continued at the same time-points as in the pretreatment phase. Results Mean pretreatment IOP in all cats was 18.46 ± 2.99 mmHg. Mean IOP decreased significantly ( P < 0.0086) in all treatment groups compared to pretreatment values (group A: 16.40 ± 0.49 mmHg, group B: 16.04 ± 0.49 mmHg, group C: 17.76 ± 0.49 mmHg). IOP did not decrease in control group D (18.55 ± 0.49 mmHg). The difference in IOP between treatment groups (A, B, C) was not statistically significant, but comparison of IOP between each treatment group and the control group was statistically significant (A–D; P = 0.0057; B–D, P = 0.0012; C–D, P = 0.0212). Conclusion Topical 2% dorzolamide significantly lowers IOP in normal cats but the effect is mild. Concomitant application of 2% dorzolamide and 0.5% timolol does significantly decrease IOP, but the effect is not significantly greater than q 8 h administration of dorzolamide alone. [ABSTRACT FROM AUTHOR]