The small (30S) subunit of prokaryotic ribosomes can assume any of a wide range of tilt positions on the specimen support. Correspondence analysis should make it possible to order views appearing in the electron micrograph according to the angle of tilt.231 individual windowed images from two micrographs showing negatively stained 30S subunits from E. coli ribosomes were subjected to multireference alignment. Correspondence analysis yielded six morphologically significant factors of variance. The second of these related to variations in stain concentrations, which are irrelevant at the level of gross morphology. The coordinates for each image in five-dimensional space (relating to factors 1,3,4,5, and 6) were subjected to a nonlinear mapping algorithm, which calculated an optimal two-dimensional map.The resulting distribution (Fig 1) consisted of two clusters, one of rightfacing, the other of left-facing views. Subaverages along the outer margin of the cluster on the left showed the particle in a range of typical views.