Pulsed dye laser lithotripsy has been used in the treatment of urinary calculi. We compared the efficacy of 2 pulsed dye lasers with different pulse durations in lithotripsy. A total of 20 pairs of human kidney stones was matched by size and composition, and randomized for laser lithotripsy under identical in vitro conditions. Each stone received 150 shocks at sequential energy settings between 40 and 140 mJ. while in a laser fiber compatible stone basket until complete fragmentation occurred. Stone fragments were separated by size and weight. We found that the laser with the shorter pulse duration fragmented stones with less total energy and produced fewer fragments greater than 3.35 mm. The differences were statistically significant.