We measured the mineral content of urinary tract stones by dual photon absorptiometry, which is widely used for the analysis of bone mineral content, and compared the values of the stones by dual photon absorptiometry (DPA values) with the results of an in vitro fracture study as well as those of an in vivo extracorporeal shock wave lithotripsy treatment study. The results of a preliminary experiment showed that the DPA values of 20 urinary tract stones reflected actual stone mineral content. As a result of the in vitro fracture study, the DPA value calculated by volume of a struvite stone, which was the most easily disintegrated, was the lowest (0.53 g/cm3). The DPA values of calcium oxalate monohydrate and apatite stones, which poorly disintegrated, were the highest (0.98, 1.01 g/cm3). The DPA value of calcium oxalate dihydrate, which moderately disintegrated, was 0.86 g/cm3. By the in vivo extracorporeal shock wave lithotripsy treatment study, the total DPA values of stones measured before extracorporeal shock wave lithotripsy treatment in 12 patients were 0.73 +/- 0.34 g in successful cases and 1.92 +/- 0.43 g in unsuccessful cases with a significant difference between the two (p less than 0.05). These results showed that the measurement of stone mineral content by dual photon absorptiometry was useful in predicting the fragility of stones against shock waves before performing extracorporeal shock wave lithotripsy treatment for patients with urinary tract stones.