The cesium salt of R, R-(-)-trans-l, 2-cyclohexane-diaminetetraacetatocobaltate(III), Δ-(+)546-Cs[Co(R, R(-)-CDTA)], Δ-Cs[Co(R, R(-)CDTA)]), provides a compound which can be used for calibration of circular dichrometers in the visible region. Δ-Cs[Co(R, R(-)CDTA)] has three major circular dichroism (CD) maxima at 593 nm, 527 nm, and 240 nm. The molecular ellipticities, [], at 593 nm, 527 nm, and 240 nm are -4490 ± 40, 5720 ± 40, and -47, 900 ± 300 deg cm2dmol−1, respectively. The CD maxima in terms of Δε at 593, 527, and 240 nm are -1.36 ± 0.01, 1.73 ± 0.01, and -14.5 ± 0.1 l cm−1mol−1, respectively. Optical rotatory dispersion (ORD) and ultraviolet-visible absorption data has also been obtained for this compound.