A preliminary report on the thymidine labeling indices and kinetics of cell proliferation in selected Morris hepatomas.

The 1 hour thymidine labeling indices have been determined for 8 hepatomas which have growth rates which vary by a factor of 14. The indices for these tumors vary only by a factor of 4. Little correlation was found. Preliminary results have been obtained on the kinetics of cell proliferation of the rapidly growing Hepatoma H-35tc(2). The tumor transfer time is 0.7 months and the growth rate is 7.0 cm. per month. The calculated values for times in different phases of the cell cycle for H-35tc(2), assuming a log normal distribution for phase duration, were as follows: T(g1) (Gap I)-11.0 hours; T(s) (DNA synthetic period)-6.6 hours; T(g2) (Gap II)-4.2 hours; T(m) (mitotic time)-0.4 hours. Therefore, the total time, T(c), for one cell cycle was calculated to be 22.2 hours. The potential doubling time was calculated to be 43 hours. The GF (growth fraction) was estimated to be 53 per cent which would suggest that approximately one-half the total cell population is nonproliferating.