The aim of the study was to compare the renal citrate excretion and the degree of urine saturation with calcium oxalate in patients with active calcium oxalate urolithiasis and in healthy subjects under basal conditions and after alkalization. There were 20 women before menopause with calcium stone disease aged 33.5 +/- 7.1 in the first group and 20 healthy women aged 32.3 +/- 7.6 in the second one. Sodium bicarbonate was administrated intravenously in a dose 16.8 g during 2 h. 24h excretion of calcium, magnesium and citrate, the degree of urine saturation with calcium oxalate and pH of urine before and after alkalization were evaluated. Hypocitraturia occurred in 45% of patients under basal conditions. The degree of urine saturation with calcium oxalate was significantly higher in women with nephrolithiasis (p < 0.01). A significant increase of citrate excretion (p < 0.001) and a decrease of calcium excretion (p < 0.05) after alkalization took place in both groups. The degree of urine saturation with calcium oxalate decreased significantly in patients with urolithiasis and in healthy subjects. During acute alkalosis, induced by sodium bicarbonate, increase of citrate excretion was observed in patients with urolithiasis in spite of hypocitraturia under basal conditions. This indicates that kidney function following alkalization is normal in "stone kidney". Significantly decreased saturation of urine with calcium oxalate was due to the decrease of calcium excretion and the increase of citrate excretion. In conclusion, the results show that the use of alkalizing factors in prevention of recurrent calcium urolithiasis is justifiable.