Abstract [ 3H]Prostaglandin E 2 (PGE 2) binding sites were 10-told enriched from a porcine fundic mucosal homogenate by differential centrifugation and subsequent discontinuous sucrose gradient separation. PGE 2 bound with an activation energy of 66 kJ/mol to a single class of sites with an affinity of 1.5 ± 0.4 nM and a capacity of 274 ± 76 fmol/mg protein. There was no indication for any cooperativity between the binding sites. Kinetic analysis revealed a k on of 3 × 10 5 M × s −1 at 30°C and pH 5.5. Dissociation was biphasic with an initial rapid (k off = 10 −3 s −1) and a subsequent slower phase (k off = 4 × 10 −5 s −1), presumably reflecting the existence of two interchangeable forms of [ 3H]PGE 2 binding sites. The rank order of affinity for other prostanoids (PGE 2 > PGE 1 > PGA 2 > iloprost (PGI derivative) > PGF 2 α > PGB 2 > PGD 2) is discussed against the background of the recently postulated E-type receptors in the stomach.