The serum cobalamin, serum folate, erythrocyte folate concentrations and total leucocyte and neutrophil counts have been studied in sickle cell children (with HbSS) during the steady state. There was a significant reduction in serum cobalamin concentration with significant increases in both the total leucocyte count and neutrophil differential. A relationship was also observed between the serum cobalamin and erythrocyte folate. The lowest erythrocyte folate levels were observed in patients with the lowest serum cobalamin concentration. These abnormalities are discussed in relation to the possible role of cobalamin in the synthesis of erythrocyte folate polyglutamate and possible immunological role of cobalamin among these children. These results lend support to the view that daily cobalamin supplementation along with folate (which is being given) may prove beneficial to the sickle cell patients as it may lower the frequency and severity of infections.