AbstractPhospholipase A1, A2, and C and diacylglycerol lipase activities were measured in cell sonicates after exposing confluent monolayers of porcine pulmonary artery endothelial cells to 5 ppm NO2, a toxic constituent of environmental pollution, for 24 and 48 hr. There was a significant increase (2.25‐fold) in phospholipase A1activity in 24 and 48 hr NO2‐exposed cells, whereas activities of phospholipases A2and C and diacylglycerol lipase were comparable to control cells at both time points. When endothelial cells were prelabeled with [3H]‐arachidonic acid and then exposed to NO2for 48 hr, increased counts were recovered from cell lysophospholipids with concomitant decreased recovery of counts from cell phosphatidylcholine and phosphatidylethanolamine. These results demonstrate that NO2exposure results in specific activation of phospholipa