[en] CO emission has been mapped along four strips in M51 using the 14 m Five College Radio Astronomy Observatory telescope (HPBW = 50'') in order to sample the radial distribution of molecular gas. The derived abundance of H₂ shows that three-fourths of the interstellar medium (ISM) nucleons are in H₂ rather than H I in the disk at R<10 kpc. For galactic radii 1--10 kpc, the radial distributions of CO emission, optical light from the disk, far-infrared flux, and nonthermal radio emission can be described by similar exponentials in R between 1 and 10 kpc with scale lengths approx.4 kpc. This contrasts sharply with the distribution of H I emission, which exhibits a hole in the center and a much flatter disk