Substituted 1-phenyl-3-benzazepines form a class of compounds possessing potent and selective affinity for the D1 DA receptor. 7,8-Dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF 38393) and its 6-halo analogues are potent and selective D1 receptor agonists. Recently, the 3-allyl derivatives of SKF 38393 and its analogues were described as selective D1 agonists with higher D1 efficacy and CNS potency. In order to extend these results to compounds in the 7-halo-8-hydroxy-substituted antagonist series, we have synthesized and pharmacologically characterized 3-allyl analogues of 7-substituted (Cl, Br, H) 8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepines. These 3-allyl derivatives were compared with their 3-methyl and 3-unsubstituted analogues in terms of their D1 receptor affinity and selectivity. The results have been used to generate structure-affinity relationships. The D1 receptor affinity, for 3-substitution, is found to be in the order: methyl greater than allyl greater than H. For 7-substitution, the affinity is in the order: Cl = Br greater than H. The 3-allyl compounds show affinity close to that of the parent (3-methyl) compounds while exhibiting a slightly diminished D1 selectivity. However, the greater lipophilicity of the 3-allyl compounds may enable them to cross the blood-brain barrier more readily and thereby exhibit higher in vivo CNS potency. Thus 3-allylbenzazepines have potential as high affinity selective D1 antagonists.