A noncommercial flow cytometry system was set up in a laboratory with no engineering staff attached. The system is based upon a conventional fluorescence microscope and a new flow principle reported by H. Steen and T. Lindmo (Science 204:403, 1979). A few modifications and additions have been introduced. The instrument has proven to be a high-resolution system, easy to adjust and control, giving coefficients of variation of cellular DNA down to 0.8% and of fluorescent polyethylene microspheres down to 0.9%.