Background: Bioavailability of a particular drug can vary according to the formulation used. Therefore, studies of comparative bioavailability of different formulations of a same drug are worthwhile. Aim: To compare the bioavailability of two risperidone formulations available in the Chilean market. Material and methods: The bioavailability of a local risperidone formulation (Spiron®) was compared with the original formulation of the drug (Risperdal®) in 12 healthy volunteers, aged 19±1 years. A single dose of 3 mg was given orally, using a randomized double blind protocol in two periods. Fifteen blood samples were obtained at regular intervals, until 24 h after drug administration. Risperidone plasma levels were measured by high pressure liquid chromatography. Pharmacokinetic parameters were calculated using a computer program that is independent of compartmental analysis. Results: The area under the curve of plasma concentration versus time, from 0 to infinite (ABC0-∞) and from 0 to 24 h (ABC0-24), early exposure (ABC from 0 to maximal time) and maximal plasma concentrations were significantly lower for Spiron®. Half life time and time to achieve the maximal concentration were similar for the two formulations. Conclusions: According to bioequivalence tests suggested by the Food and Drug Administration (FDA) of the United States (90% confidence interval for the difference of log transformed mean pharmacokinetic parameters), the formulations Risperdal® and Spiron®, cannot be considered interchangeable (Rev Méd Chile 2003; 131: 527-34).