Mathematical models for the analysis of pulse-cytophotometric (PCP) data are described. With computer programs based on these models the fractions of cells in G1-, S- and (G2 + M)-phase are obtained. The methods are applied to PCP-measurements of Ehrlich ascites tumor cells, human bone marrow cells and L-929-cells in culture. The results of the L-cell experiment are compared with autoradiographic results; for both methods the duration of the various phases has been calculated. Two different mathematical models for PCP-data evaluation and the autoradiographic method yielded results agreeing within statistical error. The application of the two models on different types of DNA-histograms is discussed: One model is suitable for asynchronous cell populations with a low fraction of S-phase cells, the other can be applied for partially synchronized cells and high S-phase fractions as well.