The particle size of Dow polystyrene latex 580G lot #3584, LS-057-A, and LS-063-A were recently redetermined by electron microscopy. Sample 580G had been polymerized in 1948, while both LS-057-A and LS-063-A date back prior to 1955. The lot 580G material that we examined had gradually increased in size over the years and was badly contaminated. A second generation of fine particles was present which may be of non-latex origin. On the other hand, both LS-057-A and LS-063-A showed no change in particle diameter. Both of these samples had been stored at high dilution (ca. 1.5 x 10(-4) g/cm(3)) and at room temperature. This work suggests that a low solids level is very important for archival storage, in so far as it essentially negates water loss through evaporation. The "drying out" of standard latex samples supplied in 10 cm(3) or similar quantities has long been known to limit their shelf life, and consequently the utility of these materials. Sample LS-057-A was also examined by QELS, which gives a measurement of particle diameter that is sensitive to agglomeration. This technique yielded a diameter ca. 18% larger than that obtained by TEM. However, upon re-dispersion using ultrasonication, very good agreement was obtained. Two badly sedimented Duke monodisperse latexes also gave satisfactory agreement with the manufacturer's stated diameter after ultrasonic re-dispersion, suggesting the utility of this method of re-dispersion.