Hypercoagulation and thrombotic complications associated with nephrotic syndrome (NS) are known from many years. However pathomechanism of those disturbances is not very clear. The aim of the presented study was to determine the role of platelets in hypercoagulation phenomenon in NS patients. Studies were carried out in 15 patients with NS in the course of chronic glomerulonephritis and 15 healthy volunteers. Following parameters were estimated: prothrombin, time APTT, fibrinogen, FDP, plasminogen, antithrombin III, alpha 2-antiplasmin and using Technicon H1 autoanalyser: platelet count (PLT), mean platelet volume (MPV) and PLT Mode. Additionally platelets aggregation (spontaneous and after collagen, epinephrine, ADP) was measured using Apact (Labor) aggregometer. We observed in patients with NS: a) decrease of AT III, b) slight increase (not significant) of fibrinogen, c) decrease of MPV and Mode PLT, d) increased spontaneous aggregation and sensitivity to aggregating agents. Our results suggest that: 1. Pathomechanism of hypercoagulation in NS is multifactorial. 2. Changes in morphology and function of platelets could be one of the factor playing important role in this mechanism.