From our observations, there seems to be no obvious connection between the disruption and changes in the actin and the microtubule cytoskeletons ( Figure 7) . Moreover, the same reorganization of the microtubule network occurs in cells infected with the vaccinia deletion mutants DF13L and DA36R which do not make actin tails (data not shown). The effects of vaccinia virus infection on the reorganization of the microtubule cytoskeleton were also observed in all cell lines we examined (BHK-21, C 2 C 12 , PtK2, RK 13 and Swiss 3T3) to varying degrees (data not shown). Our data show that vaccinia infection results in severe disruption of the normal morphology of the microtubule cytoskeleton.