Spectral reflectances were measured for the canopies of Pinus eiliouii seedlings that were inoculated versus non-inoculated with the ectomycorrhizal fungus Pisotithus linctorius. Reflectances of the less vigorous, non-inoculated seedlings increased substantially at visible and near-infrared wavelengths compared to the more vigorous, inoculated seedlings. An algorithm was developed to indicate the spectral regions in which reflectance was most sensitive to ectomycorrhizae. The reflectance curve of the more vigorous seedlings was used as a standard of comparison. We denote the spectral regions defined by this algorithm as regions of maximum reflectance sensitivity. Far-red and near-infrared photography filtered to the region of maximum sensitivity (700 nm) were used to enable visualization of a 'blue shift' reflectance response to decreased vigour in the non-inoculated seedlings in response to these differences of mycorrhizal development.