Significant amounts of three tRNAs are associated with the 70 S RNA of avian myeloblastosis virus (AMV). The temperatures at which they are half dissociated from the 70 S RNA in 50 mM NaCl and their respective quantities relative to 35 S RNA are: tRNAArg, 51 degree C, 1.6; tRNALys, 57 degree C, 0.7 and tRNATrp, 76 degree C, 1.0. Possible functions for the non-primer tRNAs (tRNAArg and tRNALys) were evaluated by determining the effect of their thermal dissociation on: (a) conversion of 70 S to 35 S RNA, (b) capacity of 70 S and/or 35 S RNA to be translated in vitro, and (c) capacity of 70 S and/or 35 S RNA to be reverse transcribed in vitro. Conversion of 70 S to 35 S RNA occurred with a tm of 56 degree C and is consistent with the hypothesis that tRNALys might be involved in joining two 35 S RNA subunits to form the 70 S RNA complex. There was no indication that the association of either tRNAArg or tRNALys influenced the rate or quality of translation of 70 S or 35 S RNA. A decrease in the rate at which 70 S RNA is transcribed occurs in parallel with the dissociation of tRNAArg and tRNALys.