We describe the structures and catalytic properties of several naturally occurring self‐cleaving RNA motifs that give 2′, 3′ cyclic phosphate products. The hammerhead and hairpin motifs are derived from plant pathogenic RNAs and the delta motif is part of the human hepatitis delta element. A fourth motif fromNeurosporais less well characterized. By assembling the self‐cleaving RNAs from more than one oligoribonucleotide, the cleavage reaction can be examined under a variety of conditions and catalytic turnover can be demonstrated. Mutagenesis and chemical methods to introduce modified nucleotides allowed the structural requirements to be deduced. The role of divalent cations in the catalytic mechanism is discussed.— Long, D. M., and Uhlenbeck, O. C. Self‐cleaving catalytic RNA.FASEB J.7: 25‐30; 1993.