Differential scanning calorimetry was used to study the effect of temperature, shaking, and pH on the stability of an aqueous dispersion of ethylcellulose latex particles (Aquacoat(TM), 0.3 mum in diameter) obtained by emulsion polymerization, and frequently used as an excipient in pharmaceutical formulations. Of the three factors studied, pH had the most marked effect on latex stability, followed by shaking and temperature. We conclude that differential scanning calorimetry is a reliable method for the study of factors that modify the stability of some components of pharmaceutical formulations.