To define the effect of mechanical force during vaporization of atherosclerotic tissue, commercially available thermal and thermal-optical laser probe systems were used to irradiate fresh homogenous atherosclerotic cadaveric human aorta in air. Force was applied as perpendicular pressure ranging from 5 to 40 gm at 2.0, 3.0, or 4.0 watts. Probe vaporization rate [VR] (tissue penetration in mm/sec) and vaporzation efficiency [VE] (volume of tissue vaporized/joule) were calculated for each irradiation. Probe temperatures [PT] were monitored using K-type thermocouples. The volume of carbonization surrounding each crater was used to quantify the amount of thermal damage [TD]. The following observations were made using these probe systems: (1) For the thermal system, VR was found to be constant with regard to force, but rose abruptly with increasing power from 3 to 4 watts. No significant increase in VE was observed with increasing force (ANOVA, P < 0.10). PT and TD also showed no dependence on force. (2) For the thermal-optical system, VR increased with applied force up to 30 gm, but reached a plateau or even decreased at greater forces. VE increased significantly at forces less than or equal to 20 gm (ANOVA, p < 0.05); however, at higher forces VE began to decrease. PT and TD both decreased with increasing probe force. Comparing the two probe systems revealed that VR and VE were significantly greater (ANOVA, p < 0.0001 and - < 0.005, respectively) but TD was not significantly smaller (ANOVA, p < 0.10) for the thermal-optical system compared to the thermal system. Within the range of energy settings evaluated, increasing mechanical force consistently enhanced vaporization up to 30gm of pressure when using the thermal-optical probe. Using the thermal probe system, this effect occurred abruptly when the power was increased. Thus, mechanical force seems to enhance laser recanalization, however, if much force is applied vaporizatioin efficiency starts to drop.