An inhibitor of lipoxygenase of arachidonic acid, nordihydroguaiaretic acid, shortens actin filaments, as judged by electron microscopic observation of negatively stained actin filaments, actin sedimentability and measurement of specific viscosity, at concentrations that inhibit the migration of phagocytic cells. At higher concentrations (more than 10 microM) nordihydroguaiaretic acid strikingly inhibits myosin ATPase activity. Thus nordihydroguaiaretic acid has a severe side effect on the cytoskeleton.