In the experiment shown in figure 2 , BTV-1 (m.o.i. = 1) was bound to the cells at 4uC for 40 minutes. The cells were then washed to remove unbound virus and placed at 37uC (in GMEM) to initiate infection. This allowed the addition of inhibitor to be synchronized with the start of infection. Concanamycin-A was added to the cells at the noted times. When used as a pretreatment, concanamycin-A was added for 0.5 h at 37uC before the addition of virus and remained present only during the virus binding step. Concanamycin-A was also added to other cells, either coincident with the start of infection (i.e. on shifting the cells to 37uC) or at various times after infection was initiated.