Mean occupancy values are shown in F1. There was considerable variability in the occupancy achieved within both groups. For the four subjects in the 2.5-mg group the raphe nuclei occupancy values (and binding potential at baseline and during pindolol augmentation) were as follows: 32% for subject 1 (baseline, 3.1; pindolol, 2.1), –17% for subject 2 (baseline, 3.6; pindolol, 4.2), 20% for subject 3: (baseline, 2.9; pindolol, 3.5), and 2% for subject 4 (baseline, 2.6; pindolol, 2.5). For the four subjects in the 5.0-mg group the occupancy values were more consistent: 41% for subject 5 (baseline, 5.7; pindolol, 3.3), 18% for subject 6 (baseline, 2.4; pindolol, 2.0), –2% for subject 7 (baseline, 3.4; pindolol, 3.5), and 20% for subject 8 (baseline, 3.2; pindolol, 2.5). Compared with the test-retest data for the control subjects, 2.5 mg t.i.d. of pindolol did not produce consistent occupancy at the 5-HT1A autoreceptor (mean=–1%, SD=24%) (t=–0.46, df=15, p=0.33). In comparison, the 5.0-mg t.i.d. dose led to a modest but significant occupancy of the 5-HT1A autoreceptor (mean=19%, SD=18%) (t=–2.77, df=15, p=0.007). After pindolol treatment, scores on the Hamilton Depression Rating Scale and Beck Depression Inventory showed inconsistent changes: for the group receiving 2.5 mg, the mean Hamilton score decreased from 13 to 11 and the mean score on the Beck Depression Inventory decreased from 19 to 13, and for the group receiving 5.0 mg, the mean Hamilton score fell from 21 to 12 and the mean score on the Beck Depression Inventory decreased from 24 to 23. There was no significant correlation between change in score on the Hamilton depression scale or Beck Depression Inventory and either the autoreceptor or postsynaptic receptor occupancy (data not shown). Plasma levels of pindolol were higher in the group receiving 5.0 mg t.i.d. (mean=35.1 ng/ml, range=16–61) than in the group receiving 2.5 mg t.i.d (mean=11.8 ng/ml, range=6–17); however, there was no correlation of plasma level with the occupancy achieved (r=–0.23, df=6, p=0.63).