The inhibitory effect of N- beta-(4-ethoxycarbonylphenoxy-ethyl-1-desoxynojirimycin (BAY o1248) and of N-hydroxyethyl-1-desoxynojirimycin (BAY o1099) was studied in normal men. Nine healthy volunteers (weight range of 82% to 117% of their ideal body weight) ingested a 50 g sucrose load together with placebo, 50 mg BAY m1099, or 10 mg BAY of o1248. Their substrate oxidation rate was measured by continuous indirect calorimetry during four hours. The plasma glucose and plasma insulin peaks were both significantly blunted and the late fall of glycemia reduced. Mean plasma glucose, fructose, and insulin were reduced by both drugs during the first two hours following the sucrose load and led to a decrease of the suprabasal glucose oxidation (oxidation above baseline) during the first two hours of the test. However, the total suprabasal glucose oxidation during the four hours of the test was not significantly different from that of the control. Breath hydrogen, as an index of malabsorption, was shown to increase with both 50 mg BAY m1099 and 10 mg BAY o1248, starting from the third hour. These findings are consistent with a significant delay of sucrose absorption induced by these new alpha-glycohydrolase inhibitors.