Nonlinear absorption by four polymethine dyes excited by focused radiation of a Nd:YAG laser second harmonic (532 nm) has been investigated experimentally. Good limiting effect in solutions and a polymer matrix has been demonstrated. Spectra of reverse saturable absorption on the nanosecond time scale were recorded (pump-probe experiment). Comparison of the experimental data on reverse saturable absorption with the results of theoretical quantum chemical investigation was carried out (S1 -> Sn and Т1 -> Тn absorption).