Both iron and calcium are essential for the hypoxia sensing mechanisms in the carotid body. However, trafficking of both ions in chemoreceptor cells in response to hypoxia is unclear. In the present study we seek to determine iron and calcium redistribution patterns in response to hypoxia in the cat chemoreceptor cells. Four cats were used: two each exposed to normoxia (PaO(2) = 90 mmHg) and hypoxia (PaO(2) = 20 mmHg) for 40 min. Carotid bodies were dissected, 150 nm sections made and processed for the measurements of iron and calcium content in the intracellular organelles of chemoreceptor cells with an energy dispersive X-ray spectroscopy. The results show that iron was distinctly lower in the hypoxic than normoxic chemoreceptor cells' cytoplasm. Conversely, calcium was increased in hypoxia, particularly in the nuclei and the dense-cored vesicles. These results highlight that regional distribution of iron does not coincide with calcium in glomus cells. Redistribution of both ions in response to hypoxia is congruous with their role in hypoxia-sensing. However, the exact determinants of iron/calcium redistribution patterns in glomus cells remain unsettled.