The purpose of this study was to measure the effect of alkaline intragastric pH on lower esophageal sphincter pressure (LESP) and on serum gastrin concentration in man. One hundred ten milliliters each of 0.1 N NaHCO3 and control solution were instilled into the stomach for 30 min in random order. Neither LESP nor serum gastrin were higher during the alkali instillation than during the control instillation. Individual subject's peak gastrin and peak LESP during the alkali period were not significantly higher than the corresponding basal values. We conclude that intragastric alkalinization did not increase total radioimmunoassayable serum gastrin concentration or LESP.