Glucose 6-phosphate dehydrogenase (G6PD) is the first enzyme of the pentose 
phosphate pathway. It exists in over 250 variants which are divided broadly into 
five classes on the basis of residual enzyme activity and clinical 
manifestations. The variants with reduced activity result in G6PD deficiency. 
This is inherited as an X-linked recessive disorder and occurs at a much higher 
frequency in the male than in the female. Most G6PD deficient individuals show 
no clinical abnormality under normal conditions, but acute hemolytic crisis may 
occur. Several nonhemolytic abnormalities occur as well in G6PD deficients at a 
higher frequency than in nondeficients. Several nonhemolytic abnormalities occur 
as well in G6PD deficients at a higher frequency than in nondeficients. The 
genetic, pathophysiologic, and therapeutic aspects of G6PD deficiency are 
presented; and the possibility of genetic counselling, care in blood banks, and 
benefits of education the G6PD deficients are discussed.