The relative populations of two amino-hydroxy conformers of cytosine, differing in rotation of the OH group by approximately 180 degrees , were selectively and repeatedly manipulated with narrowband, near-infrared laser light. For cytosine monomers isolated in a low-temperature Ar matrix, laser irradiations at 7013 cm(-1) and at 7034 cm(-1) were found to induce effective transformations of the two conformers into each other.