The evidence for the pathways involved in the metabolism of carbohydrates by malarial parasites is critically reviewed. In all species studied, glucose is catabolized mainly by glycolysis with little participation of the pentose-phosphate pathway. It has not been proved conclusively that there is a functioning citric acid cycle in the intraerythrocytic stages of avian plasmodia, nor is it certain that these stages of any malarial parasites use oxygen.