During the past six years the new and exciting form of light energy which is generated by the laser has undergone preliminary studies as a potential tool of the physician, biologist, and biophysicist. As occurred in the early investigations of the biological uses of x-radiation and nuclear radiation, a multidisciplined approach was required, and consequently the cooperative efforts of biologists, physicians, physicists, and research engineers have been required in the evaluation of biological applications of the laser beam. It was initially evident that the unique properties of the laser beam, namely its high degree of coherence and monochromaticity, would permit the light energy to be delivered into areas which were in the order of a few microns in diameter. This interesting possibility encouraged the coupling of such standard optical devices as the microscope with the laser for the investigation of laser reactions at the cellular level. The laser systems that