1. A survey was undertaken to determine the incidence of the sickle cell trait among two thousand one hundred and sixteen Jamaican children and adults of different racial groups. The following positives were found: average Jamaican children (Afro-Caucasian mixtures) 5.7 per cent; population of rural Jamaican village 3.9 per cent; Maroon schoolchildren 3.6 per cent; East Indian schoolchildren 0.7 per cent; Chinese children and adults 0 per cent; Caucasian schoolchildren 0 per cent; Caucasaian (Jamaican German) schoolchildren 0 per cent.
2. In the group of one thousand and sixty-seven average Jamaican children, no significant difference could be found between the different age-groups (i.e. infants, younger children, older children), or between the predominantly African and lesser Afro-Caucasian mixtures.
3. The incidence of the sickle cell trait in the other West Indian islands is noted.
4. The possible spread of the sickle cell trait from India to Africa, and its present uneven distribution in Africa is discussed.