Visibility measurements of power plant and smelter plumes were conducted as part of the 1981 VISTTA field programs by means of sensitometry of color photographic slides and teleradiometry. The results obtained with these two techniques at three wavelengths (450, 550, and 630 nm) were compared and showed good agreement for plume/sky radiance ratios, with correlation coefficients on the order of 0.9 and average absolute differences of 2 to 4 percent. The uncertainty in the plume/sky radiance ratio is about 4 percent for sensitometry. Although this value is slightly higher than the uncertainty of 2 percent previously reported for teleradiometry (Bergstrom et al., 1982), sensitometry offers the advantage of an instantaneous measurement. In contrast, a teleradiometer scan takes on the order of 15 minutes, and plume visual effects can show large variations in this short time period. (Copyright (c) 1984 Pergamon Press Ltd.)