We describe a computer program which will rapidly analyze a set of DNA histograms without further operator intervention after the initial input. The algorithm used was modified from that of Watson et al. (Cytometry 8:1-8, 1987). The program, coded in Pascal, has been implemented on two different systems. It has been tested by using simulated data and experimental data from cells labelled with bromodeoxyuridine. The program has been in use in this and other laboratories for over two years and has proved to be robust and fast and to give a reasonable approximation to the experimental data. It is particularly useful when dealing with badly perturbed DNA histograms.