Dictyostelium is a suitable experimental system in which to study the effects of mutations in actin-binding proteins on cell motility. Three cytoskeletal mutants that show distinct alterations in cell shape, chemotactic movement and cytokinesis serve to illustrate the diversity of phenotypes. Cells lacking talin, a protein which in many mammalian cell types is a constituent of focal complexes that link the actin cytoskeleton to the plasma membrane, are strongly impaired in adhesion to external surfaces. Coronin is an actin-associated protein that belongs to the WD-repeat family of proteins, which are engaged in protein-protein interactions involved in signalling pathways. Cells lacking coronin build large hyaline protrusions at their leading edge, diagnostic of an imbalance in the actin polymerization/depolymerization cycle. Cells devoid of a pair of cortexillins, which are novel members of the spectrin/alpha-actinin superfamily of actin-binding proteins, form an atypical cleavage furrow on a solid surface and fail to divide in suspension. Other mutants in which one or more actin-binding proteins have been knocked out have weaker phenotypes. With these mutants, cells need to be subjected to special conditions in order to reveal an effect on cell motility. For instance, only on weakly adhesive surfaces is a disturbance in the spatio-temporal co-ordination of protrusion and retraction of the cell body, and of the attachment to and detachment from a substratum, observed in a mutant that lacks three actin-binding proteins: alpha-actinin, 120 kDa F-actin gelation factor and severin.