Two new results on the structure of the spiral arms of M83=NGC 5236 are presented and discussed, using the nonthermal radio continuum brightness and polarization distributions as diagnostic tools. First, the radio continuum emission located along the inner eastern arm of M83, in the neighborhood of a prominent chain of H II regions near the minor axis of the galaxy, is mostly nonthermal. It is plausible that the CO emission which has been observed in this region has been Enhanced by a local

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... ease in the cosmic ray density from relatively recent supernovae. A fainter ridge of nonthermal emission is also found coincident with the dust lane just inside the chain of H II regions. Second, the distribution of the position angle of linear polarization in the neighborhood of a weak but extended H I spiral feature in the northwest part of the disk of M83 suggests that the polarization there may provide a new tracer for the flow direction of the ISM between spiral arms.