A systematic theoretical study of the CD of [poly(dA‐dT)]2 and its complexes with achiral small molecules is presented. The CD spectra of [poly(dA‐dT)]2 and of poly(dA):poly(dT) are calculated for various DNA structures using the matrix method. The calculated and experimental spectra agree reasonably well for [poly(dA‐dT)]2 but less well for poly (dA):poly (dT). The calculated CD spectrum of [poly (dA‐dT)]2 fails to reproduce the wavelength region of 205–245 nm of the experimental spectrum. This discrepancy can be explained by a magnetic dipole allowed transition contributing significantly to the CD spectrum in this region. The induced CD of a transition moment of a molecule bound to [poly (dA‐dT)]2 is also calculated. As was the case for [poly(dG‐dC)]2, the induced CD of a groove bound molecule is one order of magnitude stronger than that of an intercalated molecule. The calculations also show considerable differences between pyrimidine‐purine sites and purine‐pyrimidine sites. Both signs and magnitudes of the CD induced into ligands bound in the minor groove agree with experimental observations. © 1992 John Wiley & Sons, Inc.