A new combined differential-integral approach (CDI) has been developed, which is more accurate than commonly used pseudospherical models but not so complicated and computer time-consuming as a fully spherical model. The radiative transfer equation is solved in its integral form. The multiple-scattering source function is obtained by solving the integrodifferential radiative transfer equation in a pseudospherical atmosphere. Relative differences between the new model and the pseudospherical model for a variety of solar zenith angles, viewing angles, and azimuth angles for a set of wavelengths are presented. Furthermore, the CDI model is compared with a Gauss-Seidel spherical model (GSS) and with MODTRAN. The difference between CDI and GSS is found to be less than 2% and between CDI and MODTRAN up to 12%. ¿ 2000 American Geophysical Union