A popular theory of life's origins states that the first biocatalysts were not made of protein but were made of RNA or a very similar polymer. Experiments are beginning to confirm that the catalytic abilities of RNA are compatible with this 'RNA world' hypothesis. For example, RNA can synthesize short fragments of RNA in a template-directed fashion and promote formation of peptide, ester and glycosidic linkages. However, no known activity fully represents one presumed by the 'RNA world' theory, and reactions such as oxidation and reduction have yet to be demonstrated. Filling these gaps would place the hypothesis on much firmer ground and provide components for building minimal forms of RNA-based cellular life.