Near-infrared dyes - di- and tri-indocarbocyanine dyes and nickel dithiolenes - were synthesized and their third-order optical nonlinearities in solutions were investigated by using the degenerate four-wave mixing technique. Large third-order nonlinear optical susceptibilities with gamma values of up to 10(-29) esu were observed. The gamma value of the indocarbocyanine dyes increases with increase of conjugation length of the polymethine chain. The central ring structure in the chromophore lowers the gamma value of the indocarbocyanine dyes. With change of the substituents on the benzene ring an increase in gamma value is observed for all the asymmetric nickel dithiolenes. The order of increase of nonlinear hyperpolarizability is as follows: H < Cl < CH3 < C2H5 < CH(CH3)(2).