Interactions of elongation factor 2 (EF-2) with G-actin and F-actin in vitro were investigated using viscosimetry, gel filtration and electron microscopy. Under depolymerization conditions, at a molar ratio of 0.5:1 (EF-2/F-actin subunit), F-actin is stabilised by EF-2 and filaments depolymerize about three times slower than control solutions containing only F-actin. Filament stability is improved also when EF-2 is included in the solution in the presence of DNase I. Electron micrographs and viscosity measurements indicate that EF-2 may support small bundles with a width of 2 or 3 filaments. It was established that EF-2 interacts with G-actin in vitro, and reduces G-actin inhibition of DNase I activity when it is present at a ratio of 1:1. Results are discussed in the context of possible functional significance of the interactions.