The bovine serum album binding of streptomycin sulfate was studied in vitro using the technique of microdialysis combined with flow-injection analysis-chemiluminescence detection. The principle of the determination of streptomycin sulfate is that it increases the radiation emitted during the chemiluminescence oxidation of luminol by potassium hexacyanoferrate (III) in sodium hydroxide medium. The drug and protein were mixed in different molar ratios in 0.067 M phosphate buffer, pH 7.4, and incubated at 37 degrees C in a water bath. The microdialysis probe was utilized to sample the mixed solution at a perfusion rate of 5 mul min(-1). The concentration of unbound streptomycin sulfate in the microdialysate was determined by FIA-CL. In vitro recovery of streptomycin sulfate under experimental conditions was 22%. The data obtained by the present microdialysis-FI-CL system was analyzed using the Scatchard analysis and Klotz plot. The results show that the Scatchard plot and Klotz plot are linear, showing that studied drug has only one type of binding sites. The estimated binding parameters agreed well with literature values.