Twenty-seven tropolone derivatives were investigated for their tumor-specific cytotoxicity, using 3 normal human cells and 3 human oral tumor cell lines. Tropolone derivatives with phenolic OH group, hinokithiol, its tosylate and methyl ethers have relatively higher tumor specificity. 5-Aminotropolone showed the highest specificity, whereas 2-aminotropone and its derivatives showed little or no specificity. 5-Aminotropolone induced apoptotic cell death characterized by internucleosomal DNA fragmentation and caspase 3 activation in the human promyelocytic leukemic HL-60 cell line. ESR spectroscopy showed that 5-aminotropolone produced radical under alkaline condition, and efficiently scavenged O2- and NO produced by HX-XOD reaction and NOC-7, respectively. These data suggest that 5-aminotropolone may induce cytotoxicity by radical-mediated redox reaction.