Plasma virus RNA levels and amounts of RNA containing various genotypes in longitudinal samples from subjects on ritonavir monotherapy. Plasma RNA levels were determined by bDNA assay, and amounts of I54V, L63P/A, A71V, V77I, V82A/F, I84V, and L90M genotypes in plasma RNA, determined by differential hybridization as described in Materials and Methods, are labeled as such. Genotypes as determined by differential hybridization are presented below each plot; an asterisk represents the detection of a change from the consensus WT. Changes from the HIV-1SF2 consensus sequence determined by sequencing are enclosed in boxes embedded in the plots. Closed symbols represent values below the limit of quantitation for the bDNA assay and differential hybridization. IC90, 90% inhibitory concentration; d4T, stavudine.