Although it is well known that postjunctional α1-adrenoceptors mediate relaxation in the gastrointestinal tract there is little information on the subtypes involved. The aim of this study was to determine the subtypes of α1-adrenoceptor mediating smooth muscle relaxation in the rat isolated gastric fundus. Strips of longitudinal smooth muscle from the fundic region of the rat stomach were prepared via the method of Vane (1957) and suspended in organ baths containing physiological saline solution (PSS) for isometric recording using a Powerlab with Chart 5 software. The PSS was maintained at 37°C and gassed continuously with 95% O2 and 5% CO2. Smooth muscle strips were pre-constricted using barium chloride (1 mM) and cumulative concentration curves (CRC) to the non-selective α1-adrenoceptor agonist, phenylephrine, obtained. The effects of incubation of the tissue with various α1-adrenoceptor antagonists on the phenylephrine concentration-response curves were investigated: prazosin (non-selective), 5-methylurapidil (α1A), BMY 7378 (α1D) and indoramin (α1A and α1L). Shifts of the phenylephrine CRC were calculated for each of the antagonists and Schild plots constructed, where possible. pKB values were obtained from the Schild plots or from the Schild equation. Prazosin and 5-methylurapidil antagonised phenylephrine-induced relaxation with a pKBs of 8.1 and 8.0 respectively, indicating action of phenylephrine at a low affinity α1-adrenoceptor (α1L-). BMY 7378 at concentrations up to 1 μM failed to inhibit phenylephrine-induced relaxation, consistent with a lack of effect of phenylephrine at α1A, α1B or α1D adrenoceptors. Indoramin produced inhibition of phenylephrine with a pKB of 8.42, consistent with the published values of indoramin for α1A and α1B. These results support the conclusion that α1L-adrenoceptors mediate relaxation to phenylephrine in rat gastric fundus.