The organic crystal (S)-3-methyl-5-nitro-N-(1-phenylethyl)-2-pyridinamine has been previously identified by the powder technique as a promising nonlinear optical material. Large single crystals (3 × 3 × 2 cm3) of this material have been grown by temperature lowering of a seeded supersaturated solution in acetone. Refined refractive indices were obtained from the predicted angles of incidence of the phase-matched second harmonic signals. Second-order nonlinear optical coefficients, dij, as measured by the Maker fringe technique, are 11, 9, and 7 pm V-1 for d14, d25, and d36, respectively. The results are compared with calculations based on the oriented gas model.