The aim of this study was to investigate the effects of annealing time and addition of lactose in coating liquid formulations on the release of a model substance, methylene blue (MB), from pellets coated with Eudragit (R) RS 30 D. The microcrystalline cellulose pellets were layered with MB before coating with aqueous dispersions of Eudragit (R) RS 30 D using a Wurster-type fluidized bed coater. The coating processes and conditions were validated and optimized before the final coating. The uncoated and coated pellets were characterized for their size, MB content, morphology and MB release. The results demonstrated that a stable coating process can be developed to produce repeatable batches of pellets. The film thickness was calculated and found to be similar to those observed from scanning electron microscope. The increased annealing time led to a more coherent film. The drug release was found to vary depending on the duration of annealing time and the addition of lactose. Addition of lactose gave a faster MB release and without any initial lag period in the release profile whereas the increased annealing time slowed down the MB release and increased the lag period. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.