The effect of 5 dopamìnergic drugs, 2-Br-α-ergocryptine (CB 154), L-dopa, 1-(2-pyrimidyl)-4-piperonylpiperazine (Piribedil), amantadine and 1,3-dimethyl-5-amino-adamantan (D 145), on human growth hormone levels (hGH) was studied in 38 acromegalîc subjects. Acute administration of CB 154 (2.5 mg p.o.) in 34 patients was followed by a significant and sustained fall in plasma hGH levels; in 19 cases (55.9%) the observed fall was clearly below the ± 2 SD of the mean GH changes present in the same subjects after placebo. In patients previously shown to be responsive to CB 154, significant GH falls were also present following the single administration of L-dopa (500 mg p.o.) (9 patients) and Piribedil (100 mg p.o.) (5 patients), although CB 154 exhibited a more frequent, striking (reduction of up to 1–2 ng/ml) and long-lasting (4 h more) effect. In contrast, amantadine (200 mg p.o.) or D 145 (20 or 50 mg p.o.) did not induce significant changes in hGH levels (7 patients). These results broaden and corroborate previous findings on the hGH-lowering effect of dopamìnergic stimulation in acromegaly. The possible reason(s) for the difference in hGH response with different dopamìnergic compounds is discussed.