In a weak acidic medium, bleomycinA(5) (BLMA(5)) and bleomycinA(2) (BLMA(2)) can react with halofluorescein dyes such as erythrosine (Ery), eosin Y (EY), eosin B (EB) and Rose Bengal (RB) by virtue of electrostatic attraction and hydrophobic force to form ion-association complexes, which can result in the large-scale enhancement of resonance Rayleigh scattering (RRS) and the appearance of new RRS spectra. The increments of scattering intensity (Delta I) were directly proportional to the concentrations of bleomycin (BLM) in certain ranges. The detection limits for BLMA(5) and BLMA(2) ranged from 0.017 to 0.062 microg ml(-1). The Ery system had the highest sensitivity and its detection limit (3sigma) was 0.017 microg ml(-1) for BLMA(5) and 0.018 microg ml(-1) for BLMA(2), respectively. Using Ery as a RRS probe, a new highly sensitive method for the determination of BLM anticancer drugs has been developed. It was applied in the determination of BLMA(5) and BLMA(2) in serum and urine samples. The recovery was from 99.0% to 103.0%. In this work, the RRS spectral characteristics of the binding products and the optimum conditions of the reaction were investigated. The mechanism of ion-association reaction and the reasons of enhancement of resonance light scattering were discussed.