THE AIM: phase III multicenter open-label randomized comparative trial on efficacy and safety of calcium polystyrene sulfonate for correction of hyperkalemia in patients with renal failure not requiring dialysis compared with low potassium diet was performed for evaluation of efficacy and safety in 5 investigational sites of Russia. PATIENTS AND METHODS: the study included patients with level of potassium in the plasma 5.5 -6.5 mmol/L. Patients received calcium polystyrene sulfonate 30 g per day during 5 days and kept a low potassium diet. Control group was treated with only low potassium diet. Primary end-point was reduction in serum potassium concentration by Day 5 of treatment compared to baseline. RESULTS: 64 patients randomized to calcium polystyrene sulfonate [n = 32] and control diet therapy [n = 32] groups. There were no differences between groups in general parameters including demographic data and the characteristics of concomitant disorders. The level of potassium observed at the visit of Day 5 of treatment reduced by 0.837 ± 0.475 mmol/L in calcium polystyrene sulfonate group and by 0.497 ± 0.409 mmol/L in the diet group; the differences between the groups were statistically significant (p = 0.0434). As a confirmation of the second end-point, ratio of reaching normal potassium level probability on Day 5 of treatment compared to diet therapy group was 1,45 (95% CI 1,04 - 2,03). CONCLUSION: calcium polystyrene sulfonate provides significant reduction of serum potassium in patients with hyperkalemia with chronic kidney disease (CKD) which are not requiring dialysis; it has the favorable safety profile and tolerability.