SIV viral RNA load in plasma of controllers and progressors. Viral RNA copies per ml plasma are shown during infection with SIVmac239 or SIVmac251 until necropsy or exclusion from study. Controllers are depicted in blue, progressors in red. Mean peak viremia was similar in both groups, but from week 8 p.i. onward controllers exhibited a significantly lower viral load than progressors (P < 0.05 Mann-Whitney's U-test). The detection limit for this assay was 75 viral RNA copies per ml plasma. Viral loads of the long term infected monkeys 9045, 8644, 9794 are not shown.