Viral Load in Lactating Macaques. Viral RNA copies were measured by real-time RT-PCR from (A) peripheral blood plasma and (B) the cell-free fraction of milk samples obtained at indicated time points in each of fourteen lactating macaques. Milk samples that could be amplified by PCR, but had values calculated as ≤50 copies RNA/ml (amplifiable but not quantifiable) were indicated as having 50 copies. Samples from which viral RNA could not be amplified were indicated as having 1 copy. Early transmitters are shown in yellow, late transmitters in red and non-transmitters in blue.