A study of the effect of aromatic substitution on D1 and D2 affinity in a series of previously reported trans-l-piperazino-3-phenylindans shows similar structure-activity relationships for the two receptor sites. 6-Substituted derivatives have affinity for both receptors, and 6- chloroor 6-fluoro-substituted derivatives show preference for D1 receptors. D1 affinity and selectivity are significantly increased in a series of new piperazine ring substituted ...