The high affinity benzazepine D 1 agonists SKF 75670 and SKF 82957 labeled with C-11 were evaluated in vivo in rats as potential radioligands for imaging dopamine D 1 receptors with positron emission tomography (PET). Their in vivo pharmacological profile revealed selective binding for both tracers in rat brain regions rich in D 1 receptors such as the caudate-putamen. The more lipophilic [ 1 1 C]SKF 82957 (6-choloro-[ 1 1 C]SKF 75670) showed a higher brain uptake (more than 2-fold up to 30 min), higher specific uptake in the striatum and higher signal-to-noise ratio (striatum-to-cerebellum = 3.2 ± 0.4 for [ 1 1 C]SKF 75670 and 9.7 ± 2.5 for [ 1 1 C]SKF 82957 at 60 min post-injection) as compared to [ 1 1 C]SKF 75670. Both radiotracers exhibited high specificity and selectivity for D 1 receptors, since only D 1 competitors but not the D 2 antagonist sulpiride or the 5-HT 2 antagonist ritanserin reduced significantly their binding in the striatum with [ 1 1 C]SKF 75670 or the striatum and olfactory tubercles with [ 1 1 C]SKF 82957. Previous reports have shown that only D 1 agonists can recognize the functional high-affinity state from the low-affinity state of D 1 receptors. [ 1 1 C]SKF 75670 and especially [ 1 1 C]SKF 82957 are D 1 agonist radioligands that can potentially be used to study in vivo the functional high-affinity state of D 1 receptors using PET.