Ribosomal 5S 32P-labeled RNA was isolated from imbibing wheat embryos and digested with nuclease S1, a single-strand specific nuclease. The products of enzymic digestion were separated by polyacrylamide gel electrophoresis and identified by fingerprint analysis of their RNase T1 digestion products. The results indicate that the most sensitive portion of the molecule, and hence, the region containing the least helical structure, is close to the 5''-terminus. Similarly, the most resistant portion of the molecule is close to, but does not include, the 3''-terminus. Proposed models for the secondary structure of 5S RNA are discussed.