1. Repeated 15-min collections of gastric juice were made during the plateau of response to an intravenous infusion of histamine diphosphate 0·01 mg h−1 kg−1 and the samples measured and their electrolyte concentrations estimated. A linear relationship was found between chloride output and the volume-rate of overall secretion and between hydrogen ion output and the same rate of secretion, while a multivariate linear relationship was also found between all three variables.
2. A mathematical analysis of these results suggests that if gastric secretion consists of an acid and a non-acid component, each of fixed composition, then the acid component has the composition H = 143 mEq/l, K = 16 mEq/l, Cl = 169 mEq/l, and the non-acid component is secreted at the same rate in different subjects under these circumstances.
3. The data enable gross sampling and analytical errors to be detected; in particular, the volume-rate of secretion can be predicted from hydrogen ion concentration, better from chloride ion concentration, and best from the concentrations of both ions.
4. For single samples such predictions appear to be superior to the direct measurement of volume.