Red calcite dikes with widths of 1–3 m were formed during the middle and Upper Cretaceous within Mesozoic sedimentary carbonate rocks in the Transdanubian Range of Hungary. The dikes frequently develop a complex zonation with fine-grained dark-red calcite at their margins and purer and more coarsely crystalline calcite toward their centres. The staining material responsible for their colour is amorphous Fe-oxide-hydroxide whose amount remains below 1 %. The fluid inclusions of carbonates contain rather dilute (<3.5 NaCl eq. wt. %) solutions and frequently show boiling phenomena. The evidence of boiling makes the use of T_h data (100–190 °C) as estimates of formation temperatures possible. The T_h-salinity plot of the microthermometric data reveals that boiling, cooling and dilution processes were operating during calcite precipitation. The stable carbon and oxygen isotope compositions of calcites and hydrogen isotope compositions of inclusion waters indicate that the formation of red calcite dikes was induced by the ascent of magmatic H₂O–CO₂ fluid which suffered degassing prior to and during dike formation and was contaminated by meteoric waters originating from the neighbouring rocks. The assumed movements of the magmatic fluids fit well into the results of earlier studies which have shown direct effects of magmatic fluids around lamprophyre dikes and influences of magmatic fluids in the formation of manganese oxide ores during the Cretaceous in the area of the Transdanubian Range.