Abstract: Polymeric microparticles are used to deliver recombinagenic or mutagenic nucleic acid molecules such as donor nucleic acid alone, or in combination with triplex-forming molecules, to induce a site-specific mutation in the target DNA. Target cells endocytose the particles, releasing the nucleic acid molecules inside of the cell, where they induce mutagenesis or recombination at a target site. The examples demonstrate that triplex forming oligonucleotides, preferably PNAs, preferably in combination with a donor nucleotide molecule, can be encapsulated into polymeric microparticles, which are delivered into cells. Results demonstrate significantly greatly levels of uptake and expression, and less cytotoxicity, as compared to direct transfer of the nucleic acid molecules into the cell by nucleofection.