The chemical composition of the herb of four populations of common burstwort (Herniaria glabra L.) growing wild in the middle part of the Bug river valley was compared. The investigated populations differed significantly as to the content of saponins (3.47-5.29 g/100 g), tannins (0.75- 1.40 g/100 g) and flavonoids (620.7-1071.9 mg/100 g), but only slightly in the content of polyphenolic acids (0.64-0.84 g/100 g). The predominant phenolic acids turned out to be pyrocatechuic and p- hydroxybenzoic acids, and the main flavonoid compounds were isorhamnetin 3-rhamnoglucoside and rutin.