Comment on R.A. White's v function.

The v function has been defined for the purpose of determining the potential doubling time (Tpot) from bivariate flow cytometric data based on pulse labeling of the S-phase cells by bromodeoxyuridine (BrdUrd) or other related substances (White et al.: Cytometry 11:314-317, 1990). One of the immediate applications of that method is the derivation of the S-phase duration by using relative movement (RM) analysis (Begg et al.: Cytometry 6:620-626, 1985). With the v function the potential doubling time Tpot can be derived if exponential growth with stable age distribution and constant phase durations can be assumed. The v function is based on subpopulations of the labeled cells and depends, at least weakly, on time. I show that this function can be derived from a simpler expression based on the DNA distribution in the population, also including the possible quiescent cells. As a consequence, Tpot can be calculated from Ts (S-phase duration) and the phase fractions of the total population, i.e., without use of the v function.