We report on the integration of optical microsensors into a cell culture microchannel device. We demonstrate the possibility of measuring the glucose and oxygen concentrations in the microenvironment of the mammalian cells cultured in a microchannel device. Furthermore, cell proliferation and morphology could be monitored microscopically while these measurements were being made. Through the use of multiple sensors along the length of the microchannel, concentration gradients of various metabolites, such as oxygen, as well as the effects of cell uptake and perfusion rate of growth medium on these gradients could be studied. As such, the system allowed real-time observations of the cells' response to their chemical microenvironment. Our approach allows cell culture and cell assays to be performed simultaneously in an integrated microchannel system with potential applications as a research tool or drug screening method.