Cinodine, a broad-spectrum glycocinnamoylspermidine antibiotics, binds to DNA and irreversibly inhibits bacterial and phage DNA synthesis. Cinodine was found to inhibit the activity of Micrococcus luteus DNA gyrase in vitro, but it did not inhibit the activities of two other DNA-binding enzymes, namely, topoisomerase I and BamHI. Although we cannot yet conclude that DNA gyrase is an intracellular target of the drug, in vitro inhibition of the enzyme by cinodine appears to be specific.