The Kachari in upper Assam, a Bodo tribe whose language belongs to the Tibeto-Burman family, have a 0.5 frequency of the haemoglobin E gene (Hb beta E), the highest prevalence of an abnormal haemoglobin gene so far reported. In view of this high prevalence, the reproductive performance of 200 Kachari couples with different Hb beta genotypes and the pre-reproductive mortality of their offspring were examined. The differences of relative fertility observed were very small and there was no differential mortality of children. These findings indicate that at present there is no selection at the haemoglobin beta-chain locus in the Kachari population.