The relationship between the spectral properties of leaves and the water status of leaves from three crop species was studied under laboratory conditions. The wavelength region examined was from 800 to 2,600 millimicns. Leaf reflectivity and leaf adsorptivity were highly correlated with relative leaf water content. The relationship between leaf transmissivity and relative leaf water content was variable with wavelength. Leaf transmissivity was, however, highly correlated with leaf specific densities. Relative leaf water content was estimated from leaf reflectivity. The data indicated that a field reflectometer could be constructed and possibly used to monitor leaf water status. In field experiments leaf temperature was significantly affected by relative leaf water content, air temperature, and vapor pressure deficit. A relative leaf water content by vapor pressure deficit interaction term affected leaf temperature. Air temperature affected leaf temperature by modifying stomatical conductivities and, hence, the leaf transpiration rate. The leaf temperatures of the two soybean varieties were different, dependent upon the dryness of the air. The density of both regular color and infrared color film taken directly above the canopy was related to canopy moisture stress.