The effect of nitrogen fertilization and water stress on the spectral signature of winter wheatTriticum aestivumcv. Astral were measured with a field radiometer over two years. Spectral reflectance of the canopy has been related to the most indicative physiological parameters (nitrogen and photosynthctic pigment content, biomass, leaf area and LAI), but only a few of these parameters can be estimated independently of plant treatment.The normalized difference vegetation index seems the most powerful spectral combination with which to estimate the total area of plant leaves and LAI. The nitrogen content of plants can also be related to a linear combination of green and red canopy reflectances independently of plant treatment. Relations between canopy reflectance and other physiological parameters are not independent of plant treatment.