The healing process of the bladder wall after contact and non-contact Nd- YAG laser irradiation was studied in 18 piglets. The animals were sacrificed 1 h, and 2, 5 and 14 days after photocoagulation. The lesions were examined histologically by light and scanning electron microscopy. Immunohistochemical stains were prepared for visualization of lactate dehydrogenase. Perforation of the bladder wall was found in 2 cases where a contact probe was usee (15 W/2 s). A crater in the bladder wall resulting from tissue ablation was seer in all cases immediately after contact laser irradiation. Photocoagulatioi using a non-contact laser led to white necrosis in the bladder wall. Minima tissue ablation was evident at the highest power setting used (35 W/2 s). Afte 2 days inflammation around the lesion was marked. Inflammation with fibre blasts invading the damaged area was seen 5 days after photocoagulatioi Fourteen days after photocoagulation minor scar formation was evidei beneath the histologically normal epithelium. It is concluded that lesioi caused by contact or non-contact Nd-YAG laser photocoagulation will he within 2 weeks with minor scar formation.