Platelet secretion products may play an important role in the pathogenesis and progression of the kidney disease. Amongst the parameters describing platelet hyperactivity the measurement of spontaneous platelet aggregation (SPA) seems particularly useful. In this study SPA as well as mean platelet volume (MPV), modal platelet volume (PLT Mode) and platelet count (PLT) were investigated in 60 patients with biopsy proven primary glomerulonephritis. SPA was measured using the turbidimetric method according to Born with no enhancers added. Serum creatinine concentration (Cr), reciprocal serum creatinine concentration (1/Cr) and endogenous creatinine clearance (Cl<sub>Cr</sub>) were used for the renal function estimation. Protein and lipid profiles as well as coagulo-fibrinolytic balance were measured in parallel. The investigated group consisted of 30 non-nephrotic patients (CGN) – in 9, SPA was found (CGN-B) while 21 had SPA <10% (CGN-A), and 30 nephrotic patients (CGN+NS) – 19 with SPA (CGN+NS-B) and 11 without (CGN+NS-A). SPA was found to be a constant platelet feature in patients with chronic glomerulopathy. The group remained under observation for 36 months. 41 patients were included in the 3-year prospective study which revealed the significant influence of the blood platelet hyperaggregability on the renal disease progression. A significantly increased serum creatinine concentration, decreased 1/Cr parameter and decreased glomerular filtration rate (Cl<sub>Cr</sub>) were noted in subgroups showing SPA. A significant correlation between SPA and ΔCr/month (r = 0.41), Δ1/Cr/month (r = 0.38) as well as ΔCl<sub>Cr</sub>/month (r = 0.52) was found. The platelet activity and thus SPA can be altered by various factors: albumin and fibrinogen plasma concentrations, thrombosis activation and possibly lipoprotein metabolism disturbances. A characteristic feature of spontaneously aggregating platelet is their increased volume (MPV). Conclusion: Platelet hyperaggregation in one of nonimmunological factors stimulates the progression of glomerulonephritis.