High resolution 31P-NMR has been used for the non-invasive observation of 
metabolites and metabolic rates in blood of normal mice and of mice infected 
with Plasmodium berghei, the causative agent of malaria. 31P-NMR was used to 
quantitate levels of 2,3-diphosphoglycerate in whole cells as a function of the 
degree of parasitemia and yielded good agreement with the results of enzymatic 
assays. The time-dependence of 31P metabolites was monitored in both normal and 
infected erythrocytes, greater rates of decay of 2,3-diphosphoglycerate being 
observed in malarial blood which correlate with the level of parasitemia. Very 
high metabolic rates of infected cells render measurement of intracellular pH 
unreliable on freshly drawn whole blood. When appropriate measures are taken to 
avoid this complication, no difference is observed in the intracellular pH of 
parasitized and non-parasitized erythrocytes from infected animals. In both 
normal and parasitized mice the intraerythrocytic pH is more acidic than that of 
the suspending medium by 0.15 pH unit at 25 degrees C. Unlike free-living 
protozoa, the parasitic protozoan Plasmodium does not contain detectable levels 
of phosphonates or polyphosphates, in either whole cells or perchloric acid 
extracts thereof.