A total of 4939 apparently healthy Fijian and Indian subjects living in Fiji were tested for anaemia by determination of the microhaematocrit of a sample of capillary blood. The prevalence of anaemia during childhood varied with age but was similar for Fijians and Indians of either sex. The overall prevalences were: 0-4 years, 20.3%; 5-9 years, 3.7%; 10-14 years, 23.5%. The prevalence of anaemia among Indian women (33.3%) was substantially higher than that for Indian men (6.9%), Fijian women (8.1%) or Fijian men (6.8%). Iron deficiency was the most common cause of anaemia and was established by laboratory studies in 203 (68%) of 298 anaemic subjects who were followed up. Iron deficiency was an important aetiological factor in 91 (93%) of 98 subjects with moderate or severe anaemia. Folate deficiency was found, usually in combination with iron deficiency, in 44 or 141 anaemic indian adults were followed up. Folate deficiency was uncommon in Fijian adults and among children of either race. Two cases of nutritional vitamin B12 deficiency, one case of pernicious anaemia, 6 cases of heterozygous thalassaemia and one case of heterozygous haemoglobin E were found among the anaemic Indian subjects. No cases of vitamin B12 deficiency anaemia, thalassaemia or haemoglobinopathy were detected among the Fijians. In 5 Indians and 7 Fijians the anaemia was associated with an underlying chronic disorder. This study emphasizes that in Fiji, as in other developing countries, nutritional anaemia is prevalent among asymptomatic subjects. Iron deficiency is by far the most common cause.