Unfixed ribosomal subunits obtained by puromycin treatment at high ionic strength from free polysomes of rat liver and their dimers, ribosome monomers and free polysomes, were examined electron microscopically after negative staining with uranyl acetate. Small subunits are elongated and slightly bent prolate-shaped bodies which are viewed as straight (~ 230 Å × 140 Å) or curved profiles (230 Å × 120 Å). These images show a transverse dense line or partition, which divides them into two regions of unequal size (length ratio 1:2). Small subunits dimerize in an antiparallel fashion, joining to each other through their concave sides at the smaller regions in their surface. Large subunit profiles are of three main types, (i) Rounded profiles, ~ 230 Å in diameter, which correspond to views on a flattened face to which other large subunits or small subunits can bind, (ii) Asymmetric profiles which have the shape of a skiff. These are approximately triangular, with one flattened or concave side (~ 230 Å long), which shows a notch (~ 40 Å) towards the blunted side of the skiff, and two convex sides of unequal length, (iii) Triangular profiles more nearly equilateral than the previous ones. Of the two enantiomorphic types of large subunit profiles of type (ii), one is almost exclusively observed. Large subunit profiles types (ii) and (iii) are seen in “frontal” and “lateral” views, respectively, of the monomeric ribosome. Large subunit dimer profiles are formed by pairs of profiles (ii) or (iii). In the first case the separation between subunit profiles is oblique to the long axis of the dimer image. Two main views of the monomeric ribosome were observed. Frontal views have the small subunit visible throughout their length. The notch on the flattened side of large subunit profile type (ii) is seen as a dense spot immediately below the small subunit partition. If frontal views are oriented with the small subunit horizontally and towards the top, in most cases the small subunit partitions and the large subunit notches are to the left of the observer. In lateral views small subunits are seen as small rectangular profiles (140 Å × 120 Å) bound towards one end of the flattened side of large subunit profiles type (iii). If lateral views are oriented with the small subunit towards the top, most frequently the small subunit is to the right of the observer. Frontal and lateral views of the monomeric ribosome are interconvertible by tilting. A model was constructed which explains the images and the changes introduced by tilting. Within polysomes, lateral views of the monomeric ribosome were more frequent than in monomer samples. The strand joining ribosomes within a Polysome can be followed up to the dense spot under the small subunit partition or up to the junction between subunits.