We describe the employment of steady-state fluorescence spectroscopy coupled to epifluorescence microscopy (fluorescence microspectroscopy) for monitoring the diffusion of the lower-T-g component during heating of a binary blend of poly(n-butyl methaerylate-co-styrene) containing 9-vinylanthracene units attached as fluorescent label (nBMAS) with polystyrene. The segregation of the nBMAS was monitored by simply measuring the emission spectra over areas of a few micrometers at 40 degreesC (above nBMAS-T-g) near the interfacial region as a function of time, while the morphological changes and the flux of diffusant were readily revealed during the annealing process. The apparent diffusion coefficient, D-ap = (1.6 +/- 0.1) x 10(-6) cm(2) s(-1), was extracted from the slope of the better linear fitting from the plot of relative intensities (as integrated spectra) VS t(1/2).