The ablation rate of guinea pig skin and bovine aorta, myocardium, and liver by a CO 2 laser emitting 2- mu s-long pulses was quantified. Ablation efficiency was found to be strongly dependent on the ultimate tensile strength of the tissue; the ablation efficiency of liver is seven times that of skin. Gluteraldehyde cross linking of skin, which is known to greatly increase tissue stiffness but not significantly affect ultimate tensile strength, did not change the ablation rate. The water content of the tissues, which largely determines the optical and thermal properties, was measured and found to vary only slightly. The results demonstrate that tissue mechanical properties are important in the interpretation and modeling of pulsed laser ablation of tissue and that variations in these mechanical properties can lead to drastically different cutting rates for different tissues.