Spectrophotometric and spectrofluorimetric methods for the determination of two broad-spectrum fluoroquinolone antibacterials (ciprofloxacin and norfloxacin), either in pure form or in tablets, are described. Both methods are based on the formation of a ternary complex between palladium(II), eosin and the fluoroquinolone in the presence of methyl cellulose, as surfactant. Spectrophotometrically, under the optimum conditions, the ternary complexes showed an absorption maximum at 545 nm, with apparent molar absorptivities of 3.4 x 10(4) and 2.7 x 10(4) 1 mol-1 cm-1 and Sandell's sensitivities of 1.01 x 10(-2) and 1.12 x 10(-2) micrograms cm-2 for ciprofloxacin and norfloxacin, respectively. The solution of the ternary complex obeyed Beer's law in the concentration range 3-10 micrograms ml-1 for both quinolones. The proposed method was applied to the determination of the two drugs in pharmaceutical tablets. A fluorescence quenching method for the determination of both quinolones by forming this ternary complex was also investigated for the purpose of enhancing the sensitivity of the determination. The results obtained by the application of both procedures and the USP XXIII methods were in good agreement and statistical comparison by means of Student's t-test and the variance ratio F-test showed no significant differences between the three methods.