The relationship between canopy reflectance and ozone (O3) treatment was investigated in a field experiment with soybean growing in 3-m diameter, 2.4-m high open-top exposure chambers. The objectives were to develop an understanding of the pattern of reflectance changes induced by this air pollutant and to investigate how the changes might ultimately be related to yield. Correlations were obtained between the reflectance data and visual estimates of non-green leaf area, a widely-used technique for rating pollutant injury. Analysis of reflectance spectra taken in early September, early October, and mid-October showed O3 treatments to be highly correlated with reflectances at visible wavelengths and at near-infrared wavelengths up to about 720 nm. Early leaf senescence caused by O3 was easily measured by reflectance changes. (Copyright (c) 1988 American Society for Photogrammetry and Remote Sensing.)