One of the important disadvantages of tumescent anesthesia is the discomfort and painful sensation experienced by the patients directly associated with the subcutaneous administration of an anesthetic agent. The objective of the present study was to determine the optimal amount of 4% sodium bicarbonate to be added to the solution administered for tumescent anesthesia in order to reduce to a minimum pain sensation during the injection. Material and methods. The present double blind randomized controlled study included 74 patients presenting with CEAP class С2—С5 varicose veins disease divided in a random fashion into two groups. The patients of group A underwent endovenous laser obliteration and mini-phlebectomy under tumescent anesthesia using a 0.08% lidocaine/adrenaline solution with pH 7.1.The patients of group B were treated in a similar way with the use of a 0.08% lidocaine/adrenaline solution, pH 6.63, for tumescent anesthesia. The visual-analog scale was employed to evaluate the severity of pain during administration of the solution. Results. The two groups were comparable in terms of duration of the intervention and the volume of the solution administered. The mean pain intensity as estimated based on the visual-analog scale was 1.01±1.2 and 2.5±2.3 cm in groups A and B respectively. The difference in pain intensity between the two groups was significant (р<0,001) and amounted to 1,5 cm (95% Cl 0.68—2.3). The difference between pain sensations was equally significant (р<0.01). Five patients in group A reported the complete absence of pain sensations. All the patients in group B complained of the painful administration of the anesthetic. Intense pain (in excess of 5 cm based on VAS) in one patient of group A and in 6 ones of group B. Conclusion. The results of the present study give evidence that the increase in the pH value of the solution used for tumescent anesthesia alleviates pain associated with its administration. It is concluded that the volume of the 4% of sodium bicarbonate buffer solution added to the 0.08% lidocaine/adrenaline solution must be 142,8 ml per 1000 ml to ensure comfortable conditions of tumescent anesthesia for the patients presenting with varicose veins.