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In order to develop a practical and rapid method to measure the chromatic contrast sensitivity function (CCSF), the sweet parameter technique (Norcia and Tyler, 1985) with an iso-luminant chromatic grating was investigated to determine whether this method can be applied to both normal subjects and subjects with defective color vision. Vertical sinusoidal isoluminant chromatic gratings presented on a color monitor were used as stimuli. The two colors for the gratings were selected from the colors on the dichromatic iso-chromatic lines. Steady-state VFPs were recorded during a continuous decrease of chromatic contrast at 10%/s. The amplitudes of the VEP component at twice of the temporal frequency of the stimulus were evaluated. VEPs elicited by 6, 8, and 10 Hz temporal frequencies, and 0.5, 1, and 2 c/deg spatial frequencies were recorded. For all stimulus conditions, the VEP amplitudes reproducibly decreased with a decrease of chromatic contrast. The modified sweep parameter technique resulted in large amplitudes and reproducible CCSF curves which should be effective for measuring defective color vision.