Objective. Among the measures likely to reduce the risk of transmission of the agent causing the new variant of Creutzfeldt-Jakob disease, excluding blood donations from donors who had resided in the British Isles between 1980 and 1996 was considered. The objective of this study was to estimate the impact of an increase in the number of donations from new donors—resulting from the exclusion of donors who had resided in the British Isles (BI)—on the residual risk of HIV transmission through transfusion of labile blood products. Methods. The residual risk of HIV transmission associated with donations made during the serological window, estimated based on all donations collected in France during the 1996–1998 period, was expressed as a linear combination of the residual risks among known donors and new donors. For known donors, the estimate was based on the HIV incidence rate, and for new donors, on the "differential sensitivity testing" method. Several assumptions were made regarding donor exclusion rates ranging from -5% to -35%, resulting in seven simulations of the impact on residual risk. Results. The residual risk of HIV transmission was estimated, based on all donations collected during the 1996–1998 period, at 0.70 per 1 million donations, corresponding to between five and six donations collected during the serological window. Assuming that all donors who had visited the IBS were excluded from donation (35%) and replaced by new donors, the residual risk would rise from 0.70 to 0.86 per 1 million donations. This 24% increase would correspond to the collection, over three years, of one to two additional infectious donations. Conclusion. This analysis shows that a large-scale exclusion of donors, offset by the recruitment of new donors, would have a small but quantifiable impact on the residual risk of HIV transmission. This increase in risk was one of the factors taken into account in the decision not to exclude donors who had stayed in the Caribbean islands between 1980 and 1996. (R.A.)