A novel high-throughput method is presented based on fluorescence images of cells in a microchannel for determination of glutathione (GSH) and reactive oxygen species (ROS) inside single cells. We first present a method to determine GSH and ROS separately, in which GSH in cells is derivatized by 2,3-naphthalenedicarboxaldehyde (NDA), and intracellular ROS is labeled using dihydrorhodamine 123. The cells with either fluorescent derivatized GSH or fluorescent labeled ROS are introduced into a microchannel and fluorescence images of every moving cell in the microchannel are taken continuously using a highly sensitive thermoelectrically cooled electron-multiplying CCD. The fluorescence intensities of the images correspond to the masses of GSH or ROS. An average detection rate of 80-120 cells/min is achieved. We then propose a method for simultaneously determining GSH and ROS, in which ROS is first labeled in the cells. The labeled cells are then introduced into the whole channel and allowed to immobilize onto the glass substrate. The fluorescence images of all the cells in the channel are taken. NDA is then introduced into the channel to derivatize the GSH in the immobilized cells, and fluorescence images of all cells are taken again. An average analysis rate of similar to 20 cells/min is achieved. The masses of GSH and ROS in the single cells can be obtained from the fluorescence intensities of the images using their calibration curves. Since the cells are not lysed, there is no problem with adsorption of biological macromolecules and cellular debris on the channel wall, so that channel treatment, necessary in usual single-cell analysis techniques using CE and microchip electrophoresis, is no longer necessary. For single global cells, this method can also be used to determine the concentrations of ROS and GSH, which has not been reported previously. The concentrations of ROS and GSH in single global cells can be calculated from the determined masses and the cell volume (derived from the diameter of the round fluorescence image of the derivatized G S H). For gastric cancer cells, the concentrations of G S H and ROS are in the range 0.35 x 10(-3)-1.3 x 10(-3) mol/L and 0.77 x 10(-6)-1.5 x 10(-6) mol/L, respectively.