To understand molecular networking at the cellular level, analyses of processes and effects at the single-cell level are most appropriate. Usual biochemical or molecular biological analyses are based on integrated signals of numerous cells which differ, however, in their expression and activity profiles. Here we show that it is possible to determine different types of properties of individual cells by means of a specifically designed microfluidic device. As part of investigations to characterize the human urothelial cell line 5637 as a potential model system for studies of toxic and carcinogenic effects on urothelial cells, we use this cell line to assign cytochrome P450 activity, and expression of the enzymes involved, to individual cells. It is shown that the cell population is very heterogeneous with respect to the extent and kinetics of CYP1A1-dependent ethoxyresorufin O-deethylase (EROD). This is also true for the cells' CYP1A1 protein content. With some exceptions, the EROD activity largely coincides with the presence of CYP1A1 protein in the cells. The results obtained with the microfluidic device are promising and open up new perspectives with regard to multi-property determinations in individual cells and to studies focusing on the biochemical and molecular heterogeneity of cells.