The application of a finite difference Levenberg-Marquardt nonlinear least-squares procedure for the resoluton of overlapping peaks in Fourier transform-infrared spectra is described. Starting estimates of peak parameters utilized in the refinement are obtained from a numerically approximated second derivative spectrum which has been smoothed. Quantitative information reflecting the constituent peaks and the “goodness of fit” is displayed graphically in a procedure requiring much less than 1 min to both initiate and obtain results in a form that is readily interpreted.