Zinc finger proteins of the Cys2His2 type represent a large class of proteins that have been assumed to function by means of specific interactions with DNA. Experiments motivated by structural characteristics of zinc finger protein-DNA complexes revealed that certain zinc finger proteins bound DNA-RNA hybrids with affinities comparable to or greater than those for DNA duplexes. The interactions between the zinc finger proteins and the DNA-RNA hybrids were dependent on which strand was RNA and were sequence-specific. Thus, interactions with DNA-RNA hybrids should be considered with regard to the biological roles of zinc finger proteins.