The large (60S) and small (40S) ribosomal subunits were isolated from yeast (Saccharomyces cerevisiae), and preparations stained with uranyl acetate were imaged by transmission electron microscopy. Averages of three different projections of each subunit were obtained by computerized image processing with reproducible spatial resolutions approaching 3.0 and 3.5 nm, respectively. Similarities between the structures of these particles and those of other eukaryotic ribosomal subunits contribute to the development of a concensus model for the eukaryotic ribosome.