Tetracaine does not result in effective treatment of intractable pain caused by trigeminal neuralgia because of its short duration of effect. In a sustained release system a controlled delivery of the drug at the site of administration, would avoid successive administrations. Tetracaine hydrochloride (HCl) has been encapsulated using a technique based on the evaporation of solvent from an 0/0 emulsion, using poly(DL-lactic-co-glycolic acid) (PLGA) 50:50. Microspheres were separated into three fractions: 106-212, 212-300 and 300-425 mu m. The effects of two variables of the manufacturing method (volume of the inner phase of the emulsion and volume of surfactant added to the external phase) on the drug loading into microspheres, dissolution profiles and SEM characterization of the microspheres were evaluated. Microspheres containing tetracaine hydrochloride (up to 94% referred to the theoretical) released the drug, iota n-nu iota tro, over 35 days. Tetracaine HCl was delivered according to zero order kinetics from day 5 until the end of the release assay. The rate of drug release depended mainly on the viscosity of the discontinuous phase and on the size of microparticles. Microsphere size resulted more homogeneous when using the highest volume of the surfactant, being almost 80% of microparticles within the range 212-300 mu m.