We present a proteomic analysis of the rat carotid body (CB) preparation by comparison between normoxia and hypoxia. Proteomic investigation would be helpful to identify the stress-induced protein during hypoxia and to know what O(2) species are being sensed by CB cells. Adult Wistar rats were used, one group was kept in room air (21% O(2)) as control, and the other was kept in a Plexiglas chamber for 12 days in chronic hypoxia (10-11% inspired oxygen). A total protein extract for each lysated tissue was separated using a broad pH range no-linear IPG strip (3-10) and the second dimension was performed on a 9-16% polyacrylamide gel. Exposure to hypoxia for 12 days produced significant changes in protein expression, providing an initial insight into the mechanism underlying differences in susceptibility to hypoxia. Further investigation is needed to have an overview of the specific set of proteins present in the CB and the functions of such proteins in signal transduction and adaptation during hypoxia.