We have studied the prevalence and molecular nature of hereditary anaemias (abnormal haemoglobins, beta-thalassaemia, alpha-thalassaemia, and Glucose 6 phosphate dehydrogenase (G6PD) deficiency) in a primitive central Indian tribe, the Baiga. 43% of the population appear to be iron-deficient. Hereditary anaemia gene frequencies are, sickle cell 0.0824, G6PD deficiency (in males) 0.0457, beta-thalassaemia 0.0057, and deletional alpha-plus thalassaemia 0.65. Both -alpha 3.7 and -alpha 4.2 deletions were observed and non-deletional alpha-thalassaemia was suspected. The overall gene frequency of Xmn I+polymorphism (C-->T - 158 cap site; upstream of G gamma region) is 0.35. This polymorphism is preferentially linked to beta s genes. It appears that sickle cell disease covers a wide range of severity in the Baiga tribe based on higher mortality in the offspring of AS x AS parents (2.5/couple) compared to AA x AS (0.75/couple) and AA x AA (0.76/couple) parents. This is compatible with the high frequency of genetic modifying factors, i.e., the Xmn I polymorphism and alpha-thalassaemia. The results also indicate that "normal" red cell values must be defined for each population where thalassaemias, G6PD deficiency and iron deficiency are common.