We have observed and assigned several vibrational bands of 6 isotopomers of the CH3CN-BF3 complex in argon matrices. These include, for the parent isotopomer (CH3CN-(BF3)-B-11), the asymmetric BF3 stretch (v(13)) at 1248 cm(-1). the BF3 symmetric deformation or "umbrella" band (v(7)) at 601 cm(-1), and the C-N stretch (v(2)) at 2365 cm-1. All of these bands require both CH3CN and BF3, grow slightly upon annealing to 20 K, display consistent relative intensities across all sample conditions studied, and have isotopic shifts that agree well with ab initio predictions. We observe the v(2) band of CD3CN-BF3 at 2363 cm(-1), 17 cm(-1) to the red of a prior observation, though still only 7 cm(-1) from the frequency observed for crystalline CD3CN-BF3. The v(13) and v(7) bands, however, are shifted by about 50 and 200 cm(-1) from the corresponding bands in the crystal, respectively. In turn, this indicates that the structure and bonding of matrix-isolated CH3CN-BF3 must differ significantly from the crystalline form of the complex.