THE article by Lang et al.1suggests that the ruby crystal laser, without mode control, is incapable of producing small areas of tissue destruction, and also that the triocular microscope is not usable. In this laboratory we have been using a ruby crystal laser and a triocular microscope as a routine instrument in biological investigation. The laser, originally designed for ophthalmological coagulation2, has been modified to be easily connected to the microscope. In numerous experiments we have achieved areas of tissue destruction of < 2µ diameter, and Fig. 1 shows the effect of the pulsed ruby crystal laser beam on a gametophyte cell of the fern Osmunda cinnamomea L. It is worth remarking that we have investigated, theoretically, the temperature distribution in material irradiated by a focused laser beam in the system presented by the retina–choroid interface3. We are at present conducting a series of experiments on the volume/temperature relationships of laser irradiation in the case of homogeneous media and have shown, conclusively, the possibility of producing tissue destruction confined to the nucleus of a single cell.