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Eleven selected antibiotics in the East River, South China, were measured using high performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-EI-MS-MS). Erythromycin, roxitromycin, azithromycin, clarithromycin, sulfadimidine, sulfamethoxazole, sulfadiazine and trimethoprim were detected with frequencies of more than 75%, and average concentrations ranging from 0.9 to 67.4 ng l−1. The other three compounds’ (sulfathiazole, sulfacetamide and spiramycin) concentrations were below detection limits. In general, the concentrations of sulfonamides and trimethoprim were higher than those of macrolides. The concentrations of macrolides showed a spatial distribution pattern of delta > lower reach > middle reach (or urban area > agriculture area), while sulfonamides and trimethoprim did not have a significant spatial pattern. Principal component analysis and comparison with wastewater were further used to explore source information of the antibiotics. The results suggested that macrolides in the East River were mainly associated with domestic sewage, while sulfonamides and trimethoprim may be more related to agriculture wastewater, especially livestock industrial wastewater. It is suggested that to ensure/improve the drinking water quality in the region, a better pollution control of livestock industry in the lower and middle reaches is of critical importance. [ABSTRACT FROM AUTHOR]