Plasma envelope variants from monkeys inoculated with SIVmac251-8/95 (Fig. 8) mixed with SIVmac1A11 reference variant (V1-V2 region amplified from SIVmac1A11 plasmid DNA). Lane 1, SIVmac251-8/95 virus stock; lanes 2 to 6, IV-inoculated monkeys; lanes 7 to 11, IVAG-inoculated monkeys; lane 12, SIVmac1A11 reference variant. w1 and w2, week 1 and week 2 p.i.