A four-section pulsed fluid bed (PFB) dryer was employed in the film coating of granules. Particles of 1.28 and 1.62 mean diameter, containing, respectively, 6.8 and 9.2% of theophylline, were coated with a commercial polyvinyl acetate aqueous dispersion (Kollicoat SR 30 D, by BASF). The release profiles were related to the pulsation frequency (500 and 800 rpm), suspension flow rate (6.0 and 8.0 mL/min) and particle mean diameter (1.28 and 1.62 mm). A complete 23 factorial design was employed. Airflow rate and temperature were held constant at 500 m(3)(STP)/min and 60 degrees C, as well as the atomizing conditions. Results showed that all the studied variables influenced the drug release rate. The highest amount of drug released after 8 h of dissolution (83%) was achieved with the 1.28 mm particles, with frequency at 800 rpm and suspension flow rate at 6.0 mL/min. The lowest (37%) was achieved with the 1.62 mm particles, at 800 rpm with a flow rate of 8.0 mL/min. Both coated and uncoated beads were observed with a scanning electron microscope. The images showed that the film smoothes the particles surface but does not significantly increase the diameter. (C) 2007 Elsevier B.V. All rights reserved.