A new photometric method is described for the determination of microgram amounts of Rh(III), based on the formation of a ternary complex of the metal, eriochromcyanine R and cetylpyridinium bromide in an acetate buffer medium (pH = 3.2 - 3.6) with an absorption maximum at 600 nm. The system obeys the Lambert-Beer law for 0. 2 - 3. 2 ppm Rh(III). The mean relative standard deviation is 0. 66%, the molar absorptivity at 630 nm, the wavelength of the maximum difference between the ternary 4 solution and a solution of the reagents, is 1.2 × 104and the detection limit of the method is 7.8 μg. cm−2for A = 0. 001.