The pathogenesis of hypochromic anaemia was studied in 138 Saudi bedouin infants aged 9 months. Approximately 25 per cent had hypochromic anaemia, but less than 10 per cent had serum ferritin levels indicative of iron deficiency. A few infants had heterozygous beta-thalassaemia, but many infants with hypochromic anaemia had normal haemoglobin A2 levels together with serum ferritin levels above 20 micrograms/l. DNA analysis of cord blood taken from the hospital where the infants were born showed that the frequency of the single alpha-globin gene deletion type (-alpha 3.7) of alpha-thalassaemia is 0.13 in the bedouin population of Western Saudi Arabia. alpha-Thalassaemia probably accounts for much of the anaemia previously thought to be due to iron deficiency in Saudi infants. Studies of iron status and estimation of the frequency of genetic causes of hypochromic anaemia are important when assessing the need for widespread nutritional programmes to prevent iron deficiency and in the interpretation of reference ranges of red cell indices in populations from malarial areas.