The experiment was conducted in 2003-2004. The aim of the research was to investigate the chemical variability of three thyme species (Thymus pulegioides L., Thymus alpestris Tausch., Thymus kotschyanus Boiss. & Hohen) under „in situ” conditions. Six localities were selected and fixed by GPS. Samples of raw materials from the stands were collected, dried and chemically analysed. The content of essential oil and its chemical composition as well the content of flavonoids, tannins, polyphenolic acids and bitters were determined. The obtained results indicated significantly chemical differences between the investigated populations of Thymus species. The content of essential oil in the dry raw material ranged from 0.46 ml·100 g⁻¹ DM to 0.93 ml·100 g⁻¹ DM. The content of tannins was similar for T. pulegioides (5.44% on the average). However the content of tannins for T. alpestris ranged from 2.56% to 7.12%. The highest content of polyphenolic acids was determined in the herb of T. pulegioides (2.61%) from „Jaworzec”.