The present study reports initial experience with the argon laser LASTAC system in patients with chronic coronary artery occlusion not amenable to recanalization with conventional systems. The LASTAC system conducts focused argon laser light through an optical fiber of 200 microns which is inserted through a multiple-lumen balloon catheter. The balloon serves the purpose of coaxially positioning the optical fiber. The balloon catheter is advanced by means of a guidewire to about 2 mm proximal to the occlusive lesion. After advancing the optical fiber, in three times 10 to 20 Joules are applied. Thereafter, the optical fiber is withdrawn, the balloon deflated, the catheter system repositioned and the sequence repeated. The integrity of the system with respect to temperature increase, energy loss and contact with tissue is monitored with lens fluorescence. In 29 patients with angina pectoris and documented ischemia, 30 complete occlusions were treated. In 18 (60%), there was successful recanalization with conventional balloon dilation thereafter. The total success rate for the right coronary artery was 55%, for the circumflex artery 71% and for the left anterior descending artery 67%. With regard to complications, in one patient there was nontransmural myocardial infarction, in seven there were asymptomatic dissections, one patient required defibrillation. The value of the LASTAC system for recanalization of chronically occluded coronary arteries has not yet been fully delineated. However, the success rate of 60% in previously treatment-refractory patients as well as the fact that no perforations were incurred, is encouraging. Further assessment will require analysis of long-term results as well as comparison of other methods.