Imposing hypoxia (P-o2 = 23 mmHg) upon A549 cells elicited increased G(amil) although previous work had predicted a fall in this parameter. G(amil) appeared to be dependent upon glucocorticoid-driven gene expression, a process inhibited by ERK, an enzyme activated by oxidative stress. However, hypoxia transiently activated this enzyme and the response was blocked by glucocorticoids, showing that the rise in G(amil) occurs only if ERK activation is suppressed. Fluorimetric assays showed that lowering P-o2 elicited H2O2 formation indicating that this maneuver actually imposes oxidative stress, thus explaining how hypoxia can elicit responses normally associated with a rise in P-o2.