The increase in proviral load due to a high rate of Tax expression decreases with increasing rate of CTL lysis of infected cells. A theoretical model suggests that one explanation for the increase in proviral load associated with a high rate of Tax expression is that expression of Tax promotes cell division. The model predicts (4A) that the difference in proviral load between individuals who have high and low rates of Tax expression decreases as the CTL lysis rate increases. The experimental data (4B) are consistent with this prediction. The experimental data "change in proviral load with increased rate of Tax expression" was calculated by grouping all 16 subjects into groups of similar rates of lysis. Within each group the mean proviral load of the subjects with a high rate of Tax expression and the mean proviral load of subjects with a low rate of Tax expression was calculated. The difference between these two means is the "change in proviral load with an increased rate of Tax expression" and was plotted against the average rate of CTL lysis in that group.