PURPOSE: To evaluate the extent of tissue coagulation during interstitial laser photocoagulation (ILP) innormal bovine liver, using a diode laser unit and various parameters, and to determine whether the procedure isapplicable to clinical practice.. MATERIALS AND METHODS: Using an 18-gauge needle, experimental interstitiallaser photocoagulation (ILP) was carried out in normal bovine liver. On the basis of differing parameters, threegroups were established. For group I, a single photofiber with laser power of 1, 3 and 5 watts and an exposuretime of 60, 180, 300, 420 or 600 seconds was used. For groups II and III, four needles were fixed at a distance of1cm and 1.5cm ; in each case a needle fixation device was used, as well as a laser distributor for simultaneouslaser exposure of photofibers. As a control, four photofibers were placed as for groupIII, but to compare groups IIand III, each photofiber was exposed to a laser of 3 watts 300 seconds, without using a laser distributor. Toevaluate the range of tissue coagulation, specimens were analyzed both with regard to cross-sectional grossfindings and histopathologically . RESULTS: The largest diameter of thermal coagulation necrosis in Group I was15x15mm, and this was ball-shaped. Coalescence of coagulation between each photofiber was observed in Group II,and this was up to 25 mm in diameter. In Group III and controls, coalescence was not found, though the extent oftissue coagulation increased with increasing wattage and exposure time. The extent of charring at the center ofcoagulation also increased with increasing wattage. Smoke bubbles emanating from the coagulation area wereobserved, and during ILP involving a single photofiber, increased from 3 watts, applied for 300 seconds.CONCLUSION: Using an 8-gauge needle and a diode laser ILP, we have shown that a range of tissue coagulationacutely ablates normal bovine liver. In selective cases, the procedure could be applied to clinical trials.