Mitomycin-C (MMC) is the most frequently used agent for prevention of excessive scarring at the osteotomy site after endoscopic endonasal dacryocystorhinostomy (EEDCR), which, however, being applied during the final stage of the surgery, shows questionable effectiveness. Aim — to evaluate the effectiveness of a new administration route of mitomycin C in EEDCR. Material and methods. The study included 86 patients (95 cases) in the age range of 62.3±9 years with primary acquired nasolacrimal duct obstruction. All patients underwent P.J. Wormald modification of EEDCR and were further divided into 2 groups. In group 1, MMC was injected into the nasal cavity and lacrimal sac mucosa, while in group 2 it was applied locally according to the standard procedure. To measure tissue concentrations of MMC, mucosal biopsies were taken in patients of Group 1. Systemic absorption of MMC was studied through blood samples in both groups. Clinical efficacy was assessed in 14±5 months after surgery. Results. immediately after injection, the average tissue concentration of mitomicyn C in patients of Group 1, was 390±10 µg/g and 30 minutes later — 120±20 µg/g. No mitomycin C was found in Day 1 tissue samples and in any of the blood samples. Positive clinical results were reported in 97.9% of cases from Group 1 and in 87.2% of cases from Group 2. Conclusion. The method of injecting MMC during the final stage of EEDCR has proved clinically effective and safe and can be recommended for use in clinical practice.