The growth of a large single crystal of the new non-linear optical salt morpholinium 4-hydroxybenzoate (M4HB) is reported. Growth of crystals from dry ethanol, or 2-propanol, yields the non-centrosymmetric form belonging to space group Cc (No. 9). This is the desirable structure since it exhibits second harmonic generation (SHG). Attempts to improve solubility by using a water:ethanol co-solvent result in the total loss of SHG activity due to the formation of morpholinium 4-hydroxybenzoate dihydrate in the centrosymmetric space group P2(1)/c(No. 14). Crown Copyright