Three classes of mamalian ribosome-like structures were found to be associated with purified Pichinde virus preparations. These structures, possessing sedimentation coefficients of 80S, 60S and 40S, were sensitive to EDTA dissociation and possessed a buoyant density in caesium chloride of 1-61 g/ml, a value analogous to that displayed by BHK21 cell ribosomes. Analyses of RNA components associated with ribosomal particles of Pichinde virus established that 28S and 18S RNAs could be extracted from 80S monosomes. Similarly, 28S and 18S RNAs were derived, respectively, from 60S and 30S ribosomal subunits. Virus-specific 31S and 22S RNAs, as well as 28S and 18S RNAs, could be isolated from the heavy region of sucrose gradients. An additional 15S type of RNA, which was subsequently shown to be a component of intact virus particles, was also isolated from the heavy region.