[3H]Ouabain binding was investigated in membranes prepared from human brain, erythrocyte, and platelet. Scatchard analysis of [3H]ouabain binding to human hypothalamic membranes revealed a single class of noninteracting binding sites with an apparent affinity constant (KD) of 21 nM. Though the number of [3H]ouabain binding sites was lower in human platelets than in erythrocytes, both tissues exhibited a single class of high-affinity binding sites with an apparent KD similar to that found in human brain. Specific [3H]ouabain binding in basal ganglia tissue from patients with Huntington's disease was more than 50% lower than in tissue from age- and sex-matched controls. These results, along with previous findings in rat brain, suggest that high-affinity [3H]ouabain binding labels the neuronal form of Na, K-ATPase in human brain, and may prove useful in quantitating this enzyme in postmortem brain samples.