Concentration quenching of the 1.06-micro Nd(3+) fluorescence in glass is investigated to help determine the nature of the Nd(3+)-Nd(3+) interaction that causes quenching. The relative fluorescent efficiency vs Nd(3+) concentration is measured for thin, polished plates of glass in an apparatus designed to minimize instrumental distortion of the resulting curve. Fluorescent efficiency decreases exponentially with increasing Nd(3+) concentrations for concentrations less than 13 x 10(20) cm(-3) but deviates from the exponential at higher concentrations. Comparison between the data and theoretical curves indicates that Nd(3+) concentration quenching cannot be described by a dipole-dipole interaction, by the Perrin model, or by the Stern-Volmer model. Interactions that can describe the data are exchange interactions, multipole-multi-pole interactions of higher order than the dipole-dipole, and the Johnson-Williams model.