In this study, six sulfonamide derivatives, having documented CA IX inhibitor activity, reported by Durgun et al13 have been tested in terms of their cytotoxic effects in cancer cells having high (HT-29, HELA), low or no (MDA-MB-231) CA IX production as well as in normal cells (PNT1A, HEK-293), using the WST-1 methodology in time- and dose-dependent manner. Here, CA9 is linked to cancer.