L-771688 is a highly selective α1A-Adrenoceptor antagonist with a Ki of 0.43±0.02 nM. Specific [3H]L-771688 binding to cloned human α1A-Adrenoceptors is inhibited with high potency by subtype selective compounds, GG818 (Ki=0.026±0.002 nM) and L-771688 (Ki=0.052±0.008 nM) and subtype non-selective α1-adrenoceptor antagonists, prazosin (Ki=0.088±0.0.032 nM) and terazosin (Ki=1.8±0.65 nM). The relative amount of [3H]L-771688 (0.5 nM) binding in various rat tissue membranes is highest in submaxillary gland (9.5 pmol/g tissue), followed by brain (5.8 pmol/g tissue), vas deferens (4.3 pmol/g tissue), kidney (3.4 pmol/g tissue), heart (1.5 pmol/g tissue), urethra (1.1 pmol/g tissue) and prostate (0.88 pmol/g tissue). In contrast, low specific [3H]L-771688 binding is observed in rat urinary bladder (0.55 pmol/g tissue), liver (0.44 pmol/g tissue), aorta (0.11 pmol/g tissue) and spleen (0.11 pmol/g tissue).