We investigated the possibility that persons with sickle cell trait who reside chronically at moderately high altitude might develop impaired splenic reticuloendothelial function. Seventeen healthy young black men with sickle trait who had lived at greater than or equal to 1,609 m for greater than or equal to 10 years participated in the study along with 25 matched control subjects with normal hemoglobin. Splenic function was assessed by radionuclide liver-spleen scanning and by red cell pit counts. No evidence of impaired splenic function was found in the sickle trait group. The data suggest that long-term residence at moderately high altitude does not place persons with sickle cell trait at risk for splenic dysfunction.