Thymine nucleotide starvation is recombinagenic in Saccharomyces cerevisiae and induces formation of the 'nuclear dense body', a structure characteristic of yeast cells in meiosis. Conceivably, thymineless recombination in yeast, presumed to be mitotic, might be meiotic in nature. We have tested this hypothesis and have found that thymineless recombination can be induced in strains incapable of meiotic exchange.