The effect of duodenal ulcer healing induced by omeprazole on gastroduodenal generation of eicosanoids, platelet-activating factor (PAF), pepsinogen A, and gastrin was evaluated. Sixty patients with endoscopically proven duodenal ulcer were randomized to receive 20 mg omperazole once daily or 300 mg ranitidine at bedtime for 2 weeks. Patients whose ulcers did not heal were treated for an additional 2 weeks. Endoscopic biopsy specimens and serum samples were obtained before and after treatment. There was no significant difference in the healing rate between the two treatment modalities. At 2 weeks healing rates were 60% and 56% in the omperazole and ranitidine groups, respectively, whereas at 4 weeks the respective healing rates were 96% and 86%. Ulcer healing induced by omeprazole and ranitidine was not accompanied by significant changes in mucosal leukotriene B4 or C4 generation. Mucosal PAF significantly decreased in patients treated with omeprazole for 4 weeks. In omperazole-treated patients there was a trend towards increase in mucosal prostaglandin E2 generation which was significant in the fundus after 4 weeks of treatment. After 2 weeks of omeprazole treatment, serum gastrin and pepsinogen A levels almost doubled when compared with their pretreatment levels. In conclusion, duodenal ulcer healing with 20 mg omeprazole daily is not superior to healing rates with 300 mg ranitidine at bedtime after both 2 and 4 weeks of treatment. In omeprazole-treated subjects ulcer healing was accompanied by a significant decrease in mucosal PAF generation and increased levels of serum gastrin and pepsinogen A.