Interference-filter images of the Crab Nebula have been employed to produce a map of the He I 5876 A/H-beta line-intensity ratio over the bright filamentary structure. Calibrations with published slit spectroscopy and theoretical calculations indicate that most of the nebular gas is characterized by at least a 75 percent helium mass fraction if the lines arise from recombination. However, collisional excitation of He I lines may be appreciable. The line ratio distribution is markedly nonuniform, including a large, patchy, low-helium region near the base of the tubular jet structure and exceptionally high He I emitting areas defining an extended, broken strip across the pulsar. 23 references.