Cotton plants show mid-day wilting in July in the Imperial Valley, CA where air temperature in the afternoon often reaches 46 C (115 F) or higher. Wilting may occur even a few days after irrigation. A test of the growth regulator UCS6177, an experimental chemical designed to relieve moisture stress of cotton plants, was carried out in 1988. Two varieties, DES119 (regular leaf) and WC-12NL (okra leaf), were tested with from one to four applications, at 1.12 kg ai/ha each, at two weeks intervals, and water treated control and none-treated controls. The first application was made at first flower of plant growth stage of cotton. Leaf temperature and leaf water potential measurements were made twice each week and soil moisture content once a week for eight weeks. Lint yield was harvested from a 4 m long row (1/1000 acre) each plot. Results showed that the growth regulator slightly decreased the yield as the number of applications increased. The water control and none treated control had 897 kg/ha of lint and the four times application had 744 kg/ha. Leaf temperatures were higher than the control on four days by a maximum of 2 C. Only once did the cotton have lower leaf water potentials than the water treated control or untreated cotton. The treatments did not cause any significant differences in soil moisture. The two varieties responded to the growth regulator similarly, although DES-119 yield higher (904 kg lint/ ha) than WC-12NL (787 kg lint/ha). Interpretation is based on the theory of thermal kinetic window for the enzymatic activities of cotton advanced by Burke and his associates. The possibilities of adjuvant injury and the high rate of application under the studied condition are also discussed.