The fluoroquinolone ciprofloxacin is widely used in antimicrobial therapy. It inhibits the bacterial gyrase and in high concentrations in vitro also the functionally related eukaryotic topoisomerase-II, which resulted in genotoxic effects in several in vitro tests. In order to evaluate the relevance of these findings, ciprofloxacin was tested in vivo for genotoxic activity using the following test systems: micronucleus test in bone marrow of mice, cytogenetic chromosome analysis in Chinese hamster, dominant lethal assay in male mice and UDS tests in primary rat and mouse hepatocytes in vivo. These results are compared with already published in vitro and in vivo studies with ciprofloxacin. All in vivo genotoxicity revealed no genotoxic effect for ciprofloxacin. In addition, ciprofloxacin was found to be non-carcinogenic in two rodent long-term bioassays. Therefore, ciprofloxacin is considered to be safe for therapeutic use.