The frequency of a hereditary abnormality of erythocytes characterised by a deficiency in glucose 6 phosphate dehydrogenase and glutathione instability, has been investigated in various population groups in Israel. The highest frequencies of this abnormality have been detected among Jews from Kurdistan, Iraq and Persia. It is also relatively common in other oriental (sefardic) Jewish communities, as well as among Arabs, desert Bedouins and Druses.

Up to now only one case of this erythrocyte defect has been found among Jews of Ashkenazic origin. The same abnormality has also been found in a Sikh from Punjab.

The hereditary pattern of transmission and evidences of sex linkage are presented. The problem of expressivity of the abnormal gene in heterozygous females is discussed.

The genetical and medical importance of the research on the relations between blood groups and disease in the human populations requires a notable caution.

In the present paper the need is pointed out that the samples be representative, sufficient and homogeneous and some elements are noted which might introduce sampling biases.

Then the classic methods of analysis according to Aird, Woolf and Haldane are mentioned and their advantages and disadvantages outlined.

Finally a sequential method of analysis is presented that may be applied very easily and usefully by the researchers who might have the data directly and continuously in the hospitals.