An algorithm is presented to correct SAC-C MMRS imagery in the visible for atmospheric and surface effects. These effects are due essentially to gaseous absorption, molecule and aerosol scattering, and Fresnel and whitecap reflection. Aerosol scattering is determined from measurements in the spectral bands centered at 815 and 1,625 nm, where the ocean is assumed to be totally absorbing. The information is then extrapolated to the ocean-color bands, centered at 490, 550, and 660 nm. The algorithm's theoretical performance, evaluated for varied geometry, surface conditions, aerosol loading, and mixtures of continental and maritime aerosols, is about ±0.0005 (r.m.s) on the aerosol path reflectance. This accuracy meets the requirements for ocean-color applications, at least in open waters. The algorithm is applied to MMRS imagery acquired off the Valdes Peninsula, Argentina. Compared with SeaWiFS estimates of marine reflectance, the MMRS values are too low and noisy, especially at 660 nm. The discrepancies may be due to non-zero marine reflectance at 815 nm, radiometric calibration errors, and to the large noise in the data (lack of sensitivity in the atmospheric correction bands). The results demonstrate the potential of MMRS for quantitative ocean-color remote sensing in coastal regions of South America.