A fluid inclusion study of the hydrothermal minerals in two breccias from two wells in the Bagnote geothermal field (Italy) has provided information on the evolution of the fluids, and has also demonstrated that fluid inclusions can be utilized as geothermometers in this geothermal field. Both breccias come from reservoir zones: one (Bagnore 3bis (Bg 3bis)) was cored at a depth of 3111 m below ground level (b.g.l.), whereas the other (Bagnore 22 (Bg 22)) was ejected during a blow-out, probably from a fractured zone present between 2200 and 2300 m b.g.l. The hydrothermal cement of the breccias is mostly made up of quartz, K-feldspar, Na-rich plagiodase, calcite, chlorite and illite. Fluid inclusion studies were carried out on quartz (Bg 3bis and Bg 22 breccias) and adularia (Bg 22 breccia). Three types of fluid inclusions were recognized in the Bg 3bis breccia. Type I (liquid-rich) inclusions trapped an aqueous fluid with a CO2 concentration (1.7-2.7 mol/kg) that is significantly higher than present-day fluids (0.5 mol/kg). Type 11 (liquid-rich) inclusions formed after type 1, and trapped a fluid with less CO2 (0.6-1.0 mol/kg). Type III (vapor-rich) coexist with type I inclusions, and record an early fluid circulation under boiling conditions. The decrease of the CO, (and total gas) concentrations from type I inclusions to type 11 inclusions, and on to present-day conditions can be related to boiling with gas loss and/or mixing. Only one type of fluid inclusion (type 11), with moderate CO2 concentration (0.7-0.3 mol/kg), was found in the Bg 22 breccia. Boiling and/or mixing explain the variation of the CO2 Content in the Bg 22 reservoir fluid from inclusion formation to modern CO, concentration (0.3 mol/kg). The absence of any type I inclusions in Bg 22 breccia may be related to non-uniform CO2 concentrations in different parts of the field. Present-day temperatures (295 +/- 10degreesC for Bg 3bis and 320 +/- 110degreesC for Bg 22) are close or equal to fluid inclusion average total homogenization temperatures (around 290 degreesC for Bg 3bis and 320 degreesC for Bg 22), suggesting that fluid inclusions can be useful for estimating local temperatures when direct measurements are not available or dubious. (C) 2004 CNR. Published by Elsevier Ltd. All rights reserved.