Electron microscopy of negatively stained preparations of leucine aminopeptidase in solution revealed a few distinctive types of particle image. Analysis of these images and of their variants allows us to propose a model for LAPase† † Abbreviation used: LAPase, leucine aminopeptidase.: six subunits are arranged with 32 symmetry at the vertices of a distorted triangular prism (the structure being twisted about the 3-fold axis 30 † away from the eclipsed position). The subunits are elongated along the sides of triangles, and there are projections, connected in pairs, on each of the six subunits. Electron microscopy of LAPase crystals revealed a few types of image; tilting experiments show that most of them are different views of the same lattice.