Estimating the duration of S phase (T_S ) and the potential doubling time (T_pot ) from a single time measurement of the movement of cells using bivariate cytometry is common. However, these estimates require an assumption of the duration of G2 + M (T_G2+M ). Inspection of the measured dynamic quantities, relative movement [RM(t)], fractions of labeled divided and undivided cells (f^lu(t) and f^ld(t)) suggests that T_G2+M, T_S, and T_pot can be determined simultaneously.

An equation connecting the growth of the cell population, time, and the dynamic quantities was determined. The equation cannot be solved analytically, but accurate approximations can be used to find T_pot. From this result, the value of T_G2+M can be determined from f^ld(t), and T_S can be determined from RM(t).

Kinetic parameters obtained from single time estimates using the new method compared to those obtained from the analysis of multiple time‐point measurements of MCa‐K and MCa‐4 murine tumors are shown to be in close agreement. Moreover, estimates of T_G2+M in MCa‐4 tumors, treated with paclitaxel, provide extra information on the changes in T_G2+M. When applied to the rat R3327‐G prostate tumor model following androgen ablation, a correlation analysis of the T_pot values obtained by the new and previous single time‐point methods demonstrates that the rank order from shortest to longest T_pot values are largely preserved.

The new procedure makes direct estimation of T_G2+M possible from single time‐dynamic measurements. The results from previous studies on T_S and T_pot are largely unchanged, but extra information is now available. Cytometry 41:1–8, 2000 © 2000 Wiley‐Liss, Inc.