Aim. To compare diagnostic value of traditional methods of 24-hour esophageal and gastric pH monitoring (which are still widely used in clinical centers of the Russian Federation) and new acidity data proposed by researchers of NPP «Istok-Sistema» considering mean H+-ions concentrations in 24-hour pH test. Material and methods. Data of 24-hour esophageal and gastric pH monitoring were analyzed in 30 patients with pathological (over 14.72) DeMeester generalized score and in 30 healthy volunteers (DeMeester index less than 14.72) using conventional acidity values (median pH, rms pH, arithmetic mean pH, time percentage of pH <4, acidity index, DeMeester generalized score) and new pH data based on mean H+-ions concentrations in 24-hour pH test. New value was proposed to estimate esophageal acidity: time percentage of pH <4 calculated taking into account actual acidities (mean H+-ions concentration) of four pH-ranges (using coefficients): — not less than 1,0 — below 2,0; Results. It was found that new indicators provide more accurate determination of average daily esophageal and gastric acidity and time percentage of esophageal pH <4 compared to conventional methods. Conclusion. Daily average pH values (median pH, rms pH, arithmetic mean pH) may be followed by significant errors in assessing 24-hour gastric and esophageal acidity. Mean H+-ions concentration in the esophagus and stomach should be used to obtain true acidity. This will significantly reduce the likelihood of errors associated with effect of food intake, duodenogastric reflux (DGR) and other factors on average daily pH.