The quorum-quenching compounds brominated furanone C-30 and 5-fluorouracil inhibit the pathogenicity of the Pseudomonas aeruginosa laboratory strains PA01 and PA14; however, there is no report studying the effectiveness of these compounds for clinical isolates. Therefore, the effect of both quorum quenchers on the production of pyocyanin, elastase and alkaline protease of eight clinical strains from children was evaluated. Although both compounds were in general effective for the attenuation of these factors, three strains resistant to C-30 were found. For 5-fluorouracil, PA01 and some clinical isolates showed resistance for at least one phenotype.