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Abstract. This study investigates data on the C1, F, and S concentrations of plume-filter samples collected between 1992 and 1995 from Mount Etna. The samples were collected during eruptive and noneruptive activity and show fairly constant C1/F ratios but wide variation in the C1/S ratios. The determination of the C1/F ratio (between 5 and 14) allows an estimate of F degassing to be derived that ranges from 10 to 30% of the initial F content of the magma. The variation in the C1/S ratio fits an empirical two-stage degassing model where gas with high C1/S ratio is discharged during quiescient degassing and gas with low C1/S ratios is discharged during eruptive degassing. The typical permanent degassing occurs from a depth at which chlorine exsolution exceeds sulfur exsolution (C1/S> 1). The opposite of this behavior is observed during eruptive periods when significant sulfur degassing occurs because magma degasses at near atmospheric pressure (C1/SN0.1). The C1/S ratio in the plume, characterizing the type of degassing, has the potential to be a useful geochemical tool for monitoring the volcano.