The phospholipid polyunsaturated fatty acid (PUFA) content and the membrane fluidity of rat alveolar macrophages were modified dose‐dependently and in different ways. This was done to study the importance of both membrane characteristics for the cellular sensitivity toward ozone and nitrogen dioxide. Cells preincubated with arachidonic acid (20:4) complexed to bovine serum albumin (BSA) demonstrated an increased in vitro sensitivity versus ozone and nitrogen dioxide. The phenomenon was only observed at the highest 20:4 concentrations tested, whereas the membrane fluidity of the 20:4‐treated cells already showed a maximum increase at lower prein‐cubation concentrations.