Despite elevated baseline expression of the proliferative marker Ki-67, there was no difference in Ki-67 labeling index between infected C57BL/6 and bak-null mice at both the 6- and 48-wk postinfection time points, suggesting that the rate of increase in the number of proliferative cells was slower in bak-null mice following infection by H. felis. The gene discussed is MKI67; the disease is infection.