Plasma envelope variants in monkeys inoculated IV or IVAG with SIVmac251-8/95. Variants were analyzed in plasma collected at the first SIV-positive time point for each animal (w1, week 1 p.i.; w2, week 2 p.i.). Lane 1, SIVmac251 virus stock; lanes 2 to 6, IV-inoculated monkeys; lanes 7 to 11, IVAG inoculated monkeys; lane 12, SIVmac1A11 V1-V2 reference variant; lane 13, VSEV.