We have identified and characterized sigma receptor sites in porcine gastric fundic mucosa by receptor binding assay techniques using two highly selective radioligands of sigma receptor, (+)-[3H]N-allylnormetazocine (SKF 10,047) and [3H]1,3-di(2-tolyl)guanidine (DTG). Specific binding of (+)-[3H]SKF 10,047 and [3H]DTG in porcine gastric fundic mucosa were saturable, reversible and of high affinity and capacity with Kd: 90.5 nM, Bmax: 1058 fmol/mg of protein and Kd: 53.6 nM, Bmax: 3573.3 fmol/mg of protein, respectively. The inhibitory effects of sigma receptor ligands on specific (+)-[3H]SKF 10,047 binding decreased in the following order: haloperidol > DTG > or = (+)-3-(3-hydroxyphenol)-N- (1-propyl)piperidine (3-PPP) > (+)-SKF 10,047 > (-)-3-PPP > or = dextromethorphan > rimcazole > (-)-SKF 10,047. Specific (+)-[3H]SKF 10,047 binding sites showed stereoselectivity for stereoisomers of SKF 10,047 and 3-PPP and were highly correlated with the profile of sigma-1 sites. On the other hand, the inhibitory effects on specific [3H]DTG binding decreased in the following order: DTG > haloperidol > rimcazole > (+)-3-PPP > or = (-)-3-PPP > dextromethorphan > (+)-SKF 10,047 = (-)-SKF 10,047. Specific [3H]DTG binding sites did not show stereoselectivity and were highly correlated with the profile of sigma-2 sites. These findings indicate that porcine gastric fundic mucosa contains sigma receptor sites with the characteristic of sigma-1 sites and sigma-like sites showing several of the characteristics of sigma-2 sites (putative sigma-2 sites).