The effects of coffee and tea upon lower esophageal sphincteric (LES) function were examined in a blinded crossover study of 12 healthy subjects. Lower esophageal sphincter pressure (LESP) and lower esophageal (LE) pH were measured simultaneously by a sleeve sensor and a pH probe for 20 minutes before and 90 minutes after intragastric instillation of four test solutions, which contained either regular coffee (C), decaffeinated coffee (D), tea (T) or water (W). C and T solutions had the same caffeine content, 160 mg. As compared with control (W), LESP was significantly lower after C and T, but not after D. The data for LE pH paralleled those for LESP. Thus, the greatest number of reflux episodes occurred after T and C. Difference from control (W) was statistically significant for T but not for C. We conclude that both regular coffee and tea have adverse effects upon LES function, whereas decaffeinated coffee does not. This study provides a rational basis for limiting intake of both caffeinated coffee and tea in patients with clinically important gastroesophageal reflux.