The clinical utility of transcutaneous oxygen saturation monitoring during routine diagnostic and therapeutic esophagogastroduodenoscopy and colonoscopy was assessed in 271 consecutive patients. The mean patient age was 56 years (range 14-86 years). The mean preprocedure oxygen saturation was 94% (range 81-100%). The mean dosages of intravenous meperidine, diazepam and midazolam if administered were 50 mg, 6.4 mg and 3.3 mg, respectively. The largest mean decrease in oxygen saturation of all procedures compared to the preprocedure measurement was 3.2% (p = .0001) and occurred immediately after administration of intravenous medication and endoscope intubation. Colonoscopy and esophagogastroduodenoscopy patients experienced similar decreases in oxygen saturation. The patient's age and sex, type of procedure and physician performing the procedure did not affect the degree of desaturation. The largest mean decrease in oxygen saturation observed was less than that considered normal during sleep. The clinical value of transcutaneous oxygen saturation monitoring in routine diagnostic and therapeutic esophagogastroduodenoscopy and colonoscopy is not supported by the findings of this study.