In order to interpret data obtained from isolated Type I cells during hypoxia it is critical to know whether parameters such as intracellular pH (pHi) vary during this challenge. Multiple studies have attempted to address this issue but data are contradictory and methods poorly defined (Wilding et al. 1993; Pang and Eyzaguirre 1993). Wilding et al. used BCECF loaded, isolated Type I cells and demonstrated that ‘hypoxia’ did not cause a change in pHi. However, solutions in these experiments were gassed with 2% oxygen and recording chamber PO2 was not reported. Conversely, Pang and Eyzaguirre used pH-sensitive microelectrodes and demonstrated that single isolated Type I cells did acidify during a hypoxic challenge whereas clusters of Type I cells did not.