[en] Human platelets were labelled with aqueous ¹¹¹In-tropolonate in comparison with ¹¹¹In-oxinate. In normals the labelling efficiency with ¹¹¹In-tropolonate was higher (93%±2%) than with ¹¹¹In-oxinate (67%±8%) (P<0.05). In cases of severe thrombocytopenia, lower labelling efficiencies were obtained. In six normals a mean platelet life of 9 days ± 3 days and an initial recovery of 59%±15% were obtained. In twelve patients with trombocytopenia the mean platelet life was 4 days ± 4 days and the initial recovery was 58%±20%. The absolute uptake of radioactivity in spleen and in liver in both groups are reported. (orig.)