The binding of Artocarpus hirsuta lectin to galactose and its derivatives was examined by fluorescence spectroscopy. The intrinsic fluorescence intensity of the lectin was enhanced by 55% upon binding to methyl alpha-galactose without any change in the emission maximum (333 nm). 4-Methyl umbellifery alpha-galactopyranoside showed 100% quenching of its fluorescence intensity upon binding to the lectin without any shift in the emission maximum (373 nm). The association constant for the binding of the above sugars to the lectin decreases with increasing temperature. Methyl group in the alpha anomeric position of galactose enhanced the binding while that in the beta position reduced the binding to the lectin. Solute quenching studies of the lectin using acrylamide, potassium iodide and cesium chloride indicated that the tryptophan residues were fully accessible to the neutral quencher, while only partly accessible to the ionic quenchers.