Optical, cryometric, thermometric and microprobe investigations of primary melt and fluid inclusions in quartz and sanidine phenocrysts of Neogene rhyolite of the Stiavnica Stratovolcano (Slovakia) have been carried out. Homogenization temperatures of melt inclusions in quartz phenocrysts are from 870 °C to 970 °C. Potassium content in the melt predominates over sodium content, chlorine concentration is 0.2 wt. %. Homogenization temperatures of water-rich fluid inclusions are 125–180 °C in quartz (18 inclusions), and 160–225 °C in sanidine (20 inclusions). Melting temperatures of ice in fluid inclusions vary in the narrow interval from -1.4 to -1.9 °C, indicating a low salinity of the water-rich fluid (2.3–3.1 wt. % equiv. NaCl). The high density of water-rich fluid( from 0.86 to 0.94 g/cm³) corresponds to a high pressure of magmatic water (from 570 to 870 MPa) at the time of fluid trapping. It follows that the formation and consequent crystallization of acid magmas of the Western Carpathians took place at a depth of about 30 km.