β-Gal-NONOate is a nitric oxide (NO) donor which releases NO following activation by β-galactosidase. β-Gal-NONOate is stabile in aqueous solution at neutral and acidic pH for several hours, exhibits good water solubility, and is able to cross the cell membrane. Following enzymatic hydrolysis, β-Gal-NONOate decomposes with a half-life of six minutes at pH 5.6. β-Gal-NONOate is cytotoxic to a number of cancer cell-lines and exhibits high bactericidal activity against E. coli transformed with the β-galactosidase gene.