Although the ABO blood group of the human host has been reported to influence 
malarial infection, there have been few clinical observations on this effect. A 
hospital-based, comparative study was therefore performed to investigate the 
relationship between blood-group type and severe disease i nPlasmodium 
falciparum malaria. Overall, 243 cases of malaria (163 uncomplicated and 80 
severe) and 65 patients with severe, non-malarial infections were studied. In 
terms of ABO-blood-group composition, the patients with severe malaria were 
significantly different from the patients with the uncomplicated disease 
(P<0.001) and also from a population control described previously (P<0.0001). 
The patients with uncomplicated malaria or severe but non-malarial disease were, 
however, similar to the population control. The cases of severe malaria were 
significantly less likely to be of blood group O (P=0.0003), and significantly 
more likely to be of group AB (P<0.0001), than the patients with nonsevere 
malaria. It appears that individuals who are of blood-group O are relatively 
resistant to the severe disease caused by P. falciparum infection.