We have developed a pulmonary drug delivery system for the treatment of tuberculosis using rifampicin (RFP) encapsulated in poly-(lactic-co-glycolic acid) microspheres (RFP-PLGA MS), which is a biocompatible polymer. In this study, the behavior of RFP-PLGA MS and the metabolism of RFP were investigated after their uptake by macrophages using the rat alveolar macrophage cell line, NR8383. The prepared RFP-PLGA MS were spherical with an average diameter of 1.9microm and were taken up effectively by NR8383 cells in an energy-dependent manner. It was shown by fluorescent microscopic studies that the RPF-PLGA MS taken up by the cells were localized in phago-lysosomes and then degraded. Although a small amount of 3-formylrifamycin SV (3-FRSV) was generated by the metabolism of RFP, almost all RFP remained unchanged. It was considered, therefore, that RFP was released into the cytosol with drug potency intact. Based on these results, RFP-PLGA MS will be effective for the delivery of anti-tuberculosis drugs such as RFP, and will be a potentially useful drug delivery tool for pulmonary and possibly other tissues as well.