Abstract Bone marrow cultures in 15 Plasmodium falciparum patients were studied both during and after parasitaemia. Abnormalities were observed only in the group during parasitaemia. These abnormalities included: (1) decreased normoblastic number and cellular iron incorporation in all cases; (2) premature death of normoblasts during their development in the cultures in all cases; (3) defective haemoglobin synthesis in 3 of 11 cases (27%). A causal relationship between defective haemoglobin synthesis and degree of normoblastic destruction in the cultures was found. Marked anaemia and depressed C′ 3 level were found only in the group with defective haemoglobin synthesis. The significance of these findings is discussed.