This study is an analysis of the effects of formaldehyde, a chemical which is both recombinogenic and mutagenic, on white-ivory (wi) a highly mutable allele of the white locus of Drosophila. Formaldehyde is shown to significantly increase the reversion frequency of wi. The results of this investigation differ from earlier observations in three respects: (1) there is a positive correlation between RNA (ribonucleic acid) concentration and reversion frequency in the presence of formaldehyde, but reversion does not appear to be totally RNA dependent; (2) female germ cells are more sensitive than those of the male; and ( 3) a cluster of revertants has been recovered. These indicate that formaldehyde-induced wi reversion may involve a different mechanism than that proposed for formaldehyde-induced sex-linked lethals. Different mechanisms have been proposed to account for the induction of sex-linked lethals and for the increase in recombination. Formaldehyde-induced reversion of white-ivory follows the parameters of recombination.