Mixtures of CH3F and BF3 have been investigated, using infrared spectroscopy, at low temperatures in the gas phase (170-210 K) and in solution in liquid argon (85-110 K) and in liquid krypton (115-165 K). In all cases, the formation of a 1:1 complex CH3F . BF3 was observed. The complexation enthalpy was measured to be -16.8(5) kJ mol(-1) in liquid argon and -18.0(3) kJ mol(-1) in liquid krypton. Structural, energetic, and spectroscopic properties of the complex were calculated using ab initio methods at the MP2/6-31+G** level and are compared with the experimental data.