An analysis of dissolution of slightly soluble salts in physiological solutions in the presence of complexing ions was carried out, simulating conditions typical in human urine. It was found that DL-lysine, a normal physiological constituent of urine, acts at increased concentrations as a dissolving agent with respect to calcium oxalate (CaOX) calculi. The kinetics of dissolution of crystalline CaOX calculi in physiological solutions containing DL-lysine at different concentrations were studied, using the change in the Archimedean weight of samples immersed in the solution. The possible effect of lysine as a natural regulator of CaOX supersaturation and crystallization in human urine is also discussed.