We have developed a personal procedure for the radioimmunoassay of gastrin (lower detection limit 3 pg/ml). Using 5-fold concentrated lyophilized salivary samples, we are able to detect the basal content of gastrin immunoreactivity in saliva of normal fasting people (mean +/- SD: 1.38 +/- 0.61 pg/ml) compared to plasma gastrin (mean +/- SD: 28.88 +/- 11.00 pg/ml). We found that after meal stimulus, the value of salivary as well as plasma gastrin concentration increased (the correlation coefficient r among salivary and plasma gastrin being 0.899; p less than 0.001). We believe that gastrin appears in a very low concentration in saliva and that it is not produced by the gland, but derives probably from the serum clearance.