Information about the secondary structure of RNA is often useful when assessing the potential for certain RNAs to interact with proteins or when determining whether RNAs that are dissimilar in sequence can form the same structure. In this protocol we discuss chemical methods for RNA structure determination. These methods rely on the fact that certain reagents interact with RNA bases when they are single stranded, but do not react when the bases are involved in Watson-Crick base pairs. For example, dimethylsulfate (DMS) methylates the N1 position of adenosine, the N7 position of guanine, and the N3 position of cytosine only when these bases are in single-strand regions. Modifications of adenosine and cytosine create blocks to reverse transcriptase; accordingly, these modifications are detected as stops to primer extension. Modification of guanine does not create reverse transcriptase stops, but these modifications can be detected by cleavage of the modified RNA after borohydride reduction and aniline cleavage. Because DMS and other chemical reagents modify only single-stranded RNA, double-stranded regions are inferred by the lack of modification.