Fundus temperatures of the rhesus monkey were measured with argon laser (488 nm) irradiations that produced minimal, ophthalmoscopically visible lesions five minutes after exposure. Measurements were made with 10- to 20-mu tip diameter, copper-nickel thermocouples. Preliminary data included measurements at eight paramacular sites and seven macular sites. The threshold temperature rise was 17 to 26 degrees C for a ten-second exposure at these sites. Decreasing the exposure duration to 20 msec increased the threshold temperature rise range to the interval between 30 and 40 degrees C. The temperature measurements in the eye were compared to a computer solution of the heat conduction equation.