In this benchmark study, time-dependent density-functional theory (TDDFT) is applied to calculate one- and two-photon absorption spectra (related to linear and third-order optical responses, respectively) in a series of large donor-acceptor substituted conjugated molecules. Calculated excitation energies corresponding to one-and two-photon-absorption maxima are found to be in excellent agreement with experiment. The evaluated two-photon-absorption cross sections agree with experimental data as well. We conclude that the TDDFT approach is a numerically efficient method for quantitative calculations of resonant nonlinear polarizabilities in large organic chromophores.