Obesity and gastro-oesophageal reflux are the main predisposing factors for oesophageal adenocarcinoma. We have examined the effects of transient acid exposure and leptin on OE33 oesophageal adenocarcinoma cells. Leptin and acid individually stimulated proliferation and inhibited apoptosis and the combination was synergistic. Leptin receptor protein levels were unchanged by acid exposure. The COX-2 inhibitor NS 398 blocked the effects of acid and leptin but while both acid and leptin individually significantly increased PGE2 production and COX-2 mRNA levels, the combination was not more effective than either stimulant alone. Leptin synergistically enhanced acid-stimulated EGFR and ERK phosphorylation but did not further increase JNK or p38 MAP kinase phosphorylation. Specific EGFR and ERK inhibitors reduced the effects of leptin and acid alone and in combination. The combination of increased circulating leptin levels in obesity and transient reflux of gastric acid may promote oesophageal carcinogenesis by increasing proliferation and inhibiting apoptosis.