The 'first-generation' quinolones cinoxacin, nalidixic acid, oxolinic acid, pipemidic acid and rosoxacin and the newly developed quinolones ciprofloxacin, enoxacin, fleroxacin, norfloxacin and ofloxacin were screened in vitro at 10(-5), 10(-4) and 10(-3) M concentrations for ultraviolet (UV)-induced phototoxic effects in a photohemolysis test. At 10(-3) M, photodependent effects of norfloxacin could not be evaluated, as hemolysis occurred without irradiation. All other compounds with the exception of ciprofloxacin were found to be phototoxic at 10(-3) M and some also at 10(-4) M. Hemolysis was UV dose dependent and for all compounds most prominent after exposure to UVA-rich radiation except for fleroxacin which was most active in the UVB range. Besides fleroxacin, also oxolinic acid, pipemidic acid and rosoxacin induced hemolysis with irradiations rich in UVB. It is concluded that quinolones have to be regarded as potentially phototoxic substances. Therefore intense light exposure should be avoided during treatment with these agents.