Better understanding of root physiology may provide a foundation to help develop new techniques for enhancing crop production. Studies of nutrient assimilation have indicated the involvement of ATP, NADH, and reduced thiols (sulfhydryl containing enzymes and glutathione) in ion uptake. Other studies from our laboratory (unpublished data) have indicated an increase in ion uptake (predominantly Ca, K, and Mg) from nutrient media in response to foliar applications of a plant growth regulator, PGR-IV. Growth chamber studies were conducted on cotton (Gossypium hirsutum L. cv. DPL 50) to determine the effect of temperature and two rates of PGR-IV (48 ml/ha and 96 ml/ha) on root activity based on techniques developed to measure in vitro dehydrogenase (tetrazolium staining) and thiol (monobromobimane fluorescence) activity. The results from the tetrazolium test were then compared to data generated by computer enhanced imaging. Results from the tetrazolium test showed that temperatures above 35 C significantly decreased dehydrogenase levels (31%), while the application of PGR-IV significantly increased dehydrogenase activity 10% at the low rate and 13% at the high rate. The results as determined by computer imaging were similar to the tetrazolium test and indicated that dehydrogenase activity in the roots was significantly decreased (27%) by temperatures above 35 C while the high rate of PGR-IV significantly increased dehydrogenase activity 13%. The low application rate showed a trend only (4%) for increased activity. This was probably associated with the inability of the camera to resolve staining of very small root tips and hairs. The 12% increase in thiol activity in response to the high rate of PGR-IV was significant, but less than the increase (25%) in response to the low rate.