A number of endocytic processes are dependent on functional actin dynamics [2] . Therefore we determined if BTV-1 entry into BHK cells requires actin using cytochalasin-D which disrupts actin filaments. Cells were mock-treated, or treated with the drug and successful disruption of actin filaments confirmed by confocal microscopy after labelling the cells with Alexa-488 labelled phalloidin (data not shown). Mock or drug-treated cells were allowed to internalise BTV-1 (for 0.5 h) in the presence of the drug. The cells were then fixed and processed for confocal microscopy using PM10 to detect input virus as described above. Figure 6A and 6B show representative cells and that cytochalasin-D effectively blocked entry of BTV. Virtually all of the drugtreated cells (n.200 cells) showed a pattern of virus labelling as shown on the figure. In contrast, figure 6C and 6D show that cytochalasin-D did not inhibit uptake of 568-Aexa labelled transferrin, or 568-Alexa labelled dextran. These results show that BTV-1 uptake by BHK cells is actin-dependent and confirms that BTV-1 and transferrin enter cells via different mechanisms.