Spectrophotometric measuring techniques were used to determine the color of four corresponding shades of three brands of metal-fusing porcelain systems. The color was expressed in terms of CIE L*a*b* color coordinates. The relationship of these values to the more commonly used attributes of Hue, lightness (Value), and saturation (Chroma) respectively were discussed. The location of the porcelain shades in the color space and the direction of the color differences found between the different brands of porcelain were evaluated. Color differences for each paired comparison within each shade group were determined from the color data. These values represent the magnitude of color differences found between brands and have a direct relationship to visual perceptibility. For the brands and shades measured, the following conclusions can be made: The CIELAB color system provides an objective technique for evaluating the color of dental porcelains. Corresponding shades of different brands of porcelain can produce perceivably different colors. The perceived color differences between the brands were mostly a result of differences in all three color directions. Greater color differences were found to exist between the corresponding opaque porcelains than between the corresponding layered samples. The addition of 1 mm of body porcelain to the opaque compensated to a large extent for the greater color differences found between the corresponding opaques. The results of this study have significant clinical ramifications. Variations in optical characteristics of porcelains produced by different manufacturers add to the problem of color control in ceramic crown fabrication.(ABSTRACT TRUNCATED AT 250 WORDS)