The effect of carmoxirole, a presynaptic dopamine (DA2) receptor agonist, on blood pressure, plasma catecholamines, renin-aldosterone and atrial natriuretic peptide and the intracellular concentration and transmembrane fluxes of Na+ and K+, in erythrocytes and platelets was studied in 24 normal men, using a double-blind, parallel study design. After a run-in period of 1 week, the subjects were treated with either placebo (n = 8) or 0.5 mg carmoxirole (n = 16) once daily for 1 week. Blood pressure and heart rate were not changed during carmoxirole administration in these normal men. Surprisingly, no significant effect of carmoxirole was found on the circulating plasma concentration of noradrenaline, adrenaline or dopamine. Other hormones such as renin, aldosterone and atrial natriuretic peptide were also not changed during carmoxirole administration. No significant effect of carmoxirole could be demonstrated on the intracellular concentration of Na+, K+, Mg2+ and Ca2+ and on the transmembrane fluxes of Na+ and K+ in erythrocytes and platelets. In the carmoxirole-treated subjects (n = 16), 6 subjects reported spontaneously adverse events such as syncope, dizziness and vomiting tendencies and/or fatigue.