The following is a report of the recent Dengue Fever epidemic in Southern Taiwan. From Sept, 1988 to Nov, 1988, 76 patients were clinically diagnosed with fever, leukopenia, thrombocytopenia and other classical signs and symptoms of Dengue Fever. Among them 26 cases were proven by serology. Analysis and discussion were emphasized on the gastroduodenoscopic findings, histopathologic findings and relationship between upper gastrointestinal tract bleeding and thrombocytes, oral medication and clinical symptoms. 655 patients having undergone endoscopy within the same period were used as a control group. It was concluded that: 1) 58.5% of the Dengue Fever Group disclosed hemorrhagic gastritis in their endoscopic findings and in the control group only 8.9% was noted. 2) Patients with thrombocytes less than 50000/mmc suffered from UGI bleeding at a detection rate of around 48.6%. On the other hand, the detection rate was around 29.7% in those patients with thrombocytes over 50000/mmc. Thus a significant difference was shown (p less than 0.025). 3) The thrombocyte count decreased significantly in patients who had had oral medication before endoscopy compared to those without oral medication. The detection rate of UGI bleeding was 40.6% and 26% respectively (p less than 0.025). 4) Most upper G-I bleeding cases occurred after the 4th day of onset, especially in the group without oral medication. 5) There was no significant relationship between UGI bleeding and symptoms of epigastralgia or cutaneous eruption. 6) In cases of presenting hemorrhagic gastritis and superficial plus hemorrhagic gastritis by endoscopy, the detection rate of UGI bleeding seemed higher but there was no statistical difference.(ABSTRACT TRUNCATED AT 250 WORDS)