Second and third order nonlinear optical properties of some newly synthesized organic molecules and polymers are reported. Powder second harmonic generation efficiencies of up to 200 times urea have been realized for asymmetric donor-acceptor acetylenes. Third harmonic generation x(3)s have been determined for a series of small conjugated molecules in solution. THG x(3)s have also been determined for a series of soluble conjugated copolymers prepared using ring-openinig metathesis polymerization. The results are discussed in terms of relevant molecular and/or macroscopic structural features of these conjugated organic materials. © 1988 SPIE.