A Comparison of efficacy & tolerability of brimonidine (0.2%) versus dorzolamide (2.0%) in primary open angle glaucoma or ocular hypertension. In this open, randomized, cross over comparative study, 30 subjects of primary open angle glaucoma with IOP > 22 mmHg were taken. The patients fulfilling the inclusion criteria and after verifying the exclusion criteria were included in the study after a written informed consent. These subjects were randomized to receive brimonidine (0.2%) TDS or dorzolamide (2.0%) TDS for 4 weeks. After a wash out period of 4 weeks the subjects were crossed over to other therapy .The IOP was measured at 8.00 am before dosing and at 10.00 am i.e. 2 hours after dosing at each baseline and at the end of each treatment period. Monotherapy with brimonidine (0.2%) TDS and dorzolamide (2.0%) TDS given for 4 weeks had caused overall reduction in IOP of 5.833+2.102mmHg (23.48%) and 5.433+ 2.582mmHg (22.42%) respectively at peak levels. The difference is statistically insignificant (p>0.05). Overall monotherapy with brimonidine and dorzolamide appear to produce equivalent IOP lowering efficacy and have well tolerated adverse effect profile, although a trend was observed at 10.00 a.m. of greater brimonidine efficacy compared with dorzolamide.