Transfer RNA was isolated from HIV-I (human immunodeficiency virus- 1, HIV-2 (human immunodeficiency virus-2), HTLV-I (human T-cell leukemia virus-1), HIV- virus) and BLV, (bovine leukemia virus)- infected and -uninfected cells and the elution profiles of aminoacyl-tRNAs from infected and uninfected cells were compared by reverse phase chromatography. In each case examined, Asn-tRNA, which normally contains the highly modified Q base in the 5' position of its anticodon, was deficient in this base in infected cells. Phe-tRNA from HIV-I- and HIV-2-infected cells, in addition lacked the highly modified Wye base on the 3' side of its anticodon. Interestingly, one or both of these tRNAs occur at or near the ribosomal frameshift site in expression of the gag-pol poly protein of each retrovirus. The possible role of the hypomodified base in ribosomal frameshifting is presently being investigated.