Chicken gizzard smooth muscle vinculin, purified according to the method of Feramisco & Burridge (1980), was examined by rotary shadowing and electron microscopy. Individual vinculin molecules have two domains: a globular head with a diameter of 8.0 nm, and a tail 20 nm long. In high salt, vinculin self-associates into multimers containing two to six individual molecules. These molecules associate head to head and tail to tail, but the tail to tail association appears to be favored. Electron microscopy of the approximately 100,000 Mr major fragment of vinculin was performed. The tail region appeared to be cleaved off, making the head region less compact.