Aim — to investigate parameters of intraocular fluid outflow after phacoemulsification of cataract in patients with primary open-angle glaucoma (POAG). Material and methods. The study involved 153 cataract patients (153 eyes), most of whom also had POAG. The patients were divided into three groups: group 1 — 51 patients (51 eyes) with cataract but no glaucoma, group 2 — 51 patients (51 eyes) with cataract and early POAG, and group 3 — 51 patients (51 eyes) with cataract and advanced POAG. All of them underwent non-contact pneumatic tonometry, tonography, and tonography with vacuum compression (Glau-Test60) before and after surgery (phacoemulsification of cataract with implantation of a posterior chamber intraocular lens (IOL)). The follow-up period was 6 months. Results and discussion. Phacoemulsification surgery with IOL implantation was able to reduce intraocular pressure in non-glaucoma cataract patients by 3 to 5 mmHg in 21.57% of cases and by more than 5 mmHg in 58.8% of cases. In patients with early and advanced glaucoma, a 3 to 5 mmHg decrease occurred in 33.3% and 13.7% of cases, respectively, and a more than 5 mmHg decrease - in 49.02% and 56.9%, respectively. This reduction is due to activation of intraocular fluid outflow. Conclusion. A postoperative increase in trabecular and uveoscleral outflow has been detected in all groups. The change was more significant in non-glaucoma patients and those with early disease.