The study will determine whether K-Mag treatment will alleviate "steinstrasse" and reduce residual stone mass following extracorporeal piezoelectric lithotripsy. The proposal will test the hypothesis that K-Mag treatment would meet the above expectations, by raising urinary magnesium and citrate levels. The rise in the "inhibitors" in urine would prevent agglomeration of stone fragments. Moreover, the complexation of calcium by citrate and that of oxalate by magnesium may lead to a reduced stone mass.