Bee-collected pollen and propolis are apicultural products which are composed of nutritionally valuable substances and contain considerable amounts of polyphenol substances which may act as potent antioxidants. We wanted to show if respiratory burst within a cancer cell lines could be influenced when incubated with pollen and propolis extracts or not. Pollen and propolis extracts at concentrations of 50, 25, 12.5 and 0 mg/ml were prepared by dimethyl sulfoxide (DMSO). K-562 cell cultures and mononuclear cell (MNC) cultures prepared from a peripheral blood sample to serve as control cells were incubated with extracts for 24 h. Determination of respiratory burst was carried out by intracellular dichlorofluorescein (DCFH) test by using flow-cytometric fluorescence analysis. While about 90% and 66% fluorescence was detected at zero concentrations for both K-562 and MNC cultures, fluorescence positivity decreased (between 3.8% and 11.8%) as concentrations of both propolis and pollen extracts increased for K-562 cell culture, but unchanged (between 20% and 83%) for MNC culture. It was concluded that pollen and propolis extracts inhibit respiratory burst within cancer cell lines probably by their antioxidant potentials. (c) 2005 Published by Elsevier B.V.