Fiber tip breakage during urinary and biliary laser lithotripsy has been recognized to occur with several laser types. This phenomenon has also been seen with Q-switched Nd:YAG laser lithotripsy. Our aim was to determine the biological consequences of this event in the canine ureter and bile duct. In an excised tissue preparation, urinary and biliary stones were impacted in a canine ureter and common bile duct. Three and four hundred micron quartz laser fibers were placed in direct contact with the stone. Normal saline coaxial irrigation was initiated at 75 xal/min. A Q-switched Nd:YAG laser was activated at repetition rates from 1O-30 Hz. and pulse energies from 10-30 mJ. The tissue was sectioned and microscopic examination of the fragmentation site was performed. Histological exam revealed the persistence of large numbers of fiber fragments in the lumen and imnbedded in the epithelium at the lithotripsy site. Fragments varied greatly in size and appeared to have angular, sharp edges We conclude that irrigation can not be relied upon to remove the fiber fragments from the lithotripsy sites and that the biological consequences of fiber fragmentation may be greater than previously believed. Glass fragments "blown" into the epitheliumu will often result in glass granulomas, which may eventually cause obstruction of closed lumninal structures. This raises serious concern for the presence of any fiber breakage during laser lithotripsy.