Limited information exists about cottons (Gossypium hirsutum L.) genotypic response and techniques to quantify this response to high temperature. Growth room and field studies were used to evaluate techniques and genotypes for high temperature tolerance in cotton. Techniques tested were chlorophyll fluorescence, membrane leakage, photosynthesis, antioxidant enzyme activity, total soluble proteins, leaf carbohydrates, myo-inositol, leaf extension growth, crop growth rate and net assimilation rate. Chlorophyll fluorescence, membrane leakage, and leaf extension growth were the most practical, reliable, and sensitive techniques for quantifying cottons response to high temperature stress. The cotton plant starts showing signs of stress between 35^oC and 38^oC. Among the genotypes screened, Acala Maxxa, SG215BR, and DP444BG/RR were the most tolerant genotypes to high temperatures, and the wild type cotton was significantly more tolerant than the commercial cultivars. For improve high temperature tolerance in cotton, the introduction of wild germplasm and screening under controlled environment conditions is needed.