The activity level of acetylcholinesterase in the erythrocytes of 32 patients homozygous for sickle cell anemia was determined and compared with that of normal AA controls as well as with that of AS individuals. Acetylcholinesterase activity was markedly higher in erythrocyte membrane from SS individuals than in those from AS individuals or AA controls. Additionally, ATPase activities were also significantly higher in sickle cell erythrocytes as compared to normal cells. These higher values of acetylcholinesterase and ATPase activities in SS erythrocytes may be explained as a consequence of the abnormally high cation levels in sickle cell erythrocytes.