Hydrophilic matrix tablets were developed with acyclovir (ACV), using hypromelose and polyethylene oxide (PEO) in different concentrations. Matrix tablets obtained in each formulation were evaluated to determine the weight variation, thickness, hardness, drug content, swelling and erosion and in vitro release. The swelling and erosion studies were influenced by pH value and polymer type. The ACV release under acid conditions occurred around 12 and 6 h for PEO and hypromelose matrices, respectively. The mechanism involved in drug release was characterized by anomalous behavior for all formulations, except in 0.1 N HCl where formulations containing hypromelose demonstrated a Super Case II kinetics.Colegio de Farmacéuticos de la Provincia de Buenos Aires