The real issue in the development of oral controlled release dosage forms is not just to prolong the delivery of drugs but also to prolong the presence of dosage forms in the stomach in order to improve the bioavailability of drugs with a 'narrow absorption window'. In the present study, an anti-ulcer drug, ranitidine hydrochloride, is delivered through a gastroretentive ethyl cellulose-based microparticulate system capable of floating on simulated gastric fluid for > 12 h. Preparation of microparticles is done by solvent evaporation technique with modification by using an ethanol co-solvent system. The formulated microspheres were free flowing with good packability and encapsulation efficiencies were up to 96%. Scanning electron microscopy confirmed porous, spherical particles in the size range 300-750 mu m. Microspheres showed excellent buoyancy and a biphasic controlled release pattern with 12 h. In vivo bioavailability studies performed on rabbits and T(max), C(max), AUC were calculated and confirmed significant improvement in bioavailability. The data obtained thus suggests that a microparticulate floating delivery system can be successfully designed to give controlled drug delivery, improved oral bioavailability and many other desirable characteristics.