Twenty-four male college students were divided into two groups and served as subjects for a study which investigated the progressive effects of heat and cold on maximum isometric grip strength. One group of 12 subjects was exposed to a heating (40 degrees C) treatment, the other to a cooling (10 degrees C) treatment. Maximum isometric grip strength was measured prior to the application of treatments and again every two minutes until the end of the 30 minute treatment period. Cutaneous temperature of the contracting limb was also measured simultaneously with the maximum contractions. With cooling, cutaneous temperature was found to decrease 16.29 degrees C by the end of the treatment period. Maximum grip strength improved 8.29 percent immediately following the application of cold and then declined 14.05 percent by the end of treatment. Heating produced a 5.96 degrees C increase in cutaneous temperature, with maximum grip strength declining 17.93 percent during the first 22 minutes of treatment. This trend then reversed itself and maximum strength improved to within 91.93 percent of the pre-treatment value. The results suggest a neural, as well as mechanical, influence of temperature on muscular contractions.