In psychophysical experiments, subjects adjusted the test part of the Müller-Lyer figure to make it appear equal in length to the reference part of the figure in the absence and presence of luminance contrast. The illusion was measured as function of the length and internal angle of wings varying from 7 to 35 min of arc and from 40 degrees to 180 degrees, respectively. Müller-Lyer figures, 130 min of arc long with no shaft line, were generated by Cambrige Research Systems VSG2/3 and presented as stimuli on an EIZO T562 monitor with gamma correction. The CRT primary colors provided chromatic contrast between the stimulus and the background area. Prior to the experiments, the method of two-color gratings was used to detect isoluminance for each color pair. The experimental curves showed a significant increase of the illusion strength up to 1.5-2 times at isoluminance irrespective of the colors combined. The data obtained are interpreted in terms of spatial-frequency filtering and low-pass chromatic filters.