Stereospecific binding sites for (+)-[3H]SKF 10,047 have been demonstrated in rat liver. These binding sites were shown to be opioid receptors of the sigma type, and this was confirmed by their binding properties: reversibility, saturability, stereospecificity, effects of ions and various pharmacological drugs on (+)-[3H]SK sigma F 10,047 binding. The authors suggest that (+)-[3H]SKF 10,047 binding sites in liver and brain are a part of novel 'sigmergic' regulatory system.