The alkaline preparation of prokaryotic plasmids (Birnboim and Doly, 1979) has been here adapted to yeast. By simple denaturation and renaturation steps we recovered, from Saccharomyces cerevisiae and Schizosaccharomyces pombe, a population of nucleic acid molecules highly enriched in circular forms. In S. cerevisiae killer strains it is possible to copurify double stranded RNA molecules. The overall recovery was estimated to be 10-30% of the total circular molecules.