A novel method for the in vitro detection of the protozoan Plasmodium, the 
causative agent of malaria, has been developed. It comprises a protocol for 
cleanup of whole blood samples, followed by direct ultraviolet laser desorption 
(LD) time-of-flight mass spectrometry. Intense ion signals are observed from 
intact ferriprotoporphyrin IX (heme), sequestered by malaria parasites during 
their growth in human red blood cells. The LD mass spectrum of the heme is 
structure-specific, and the signal intensities are correlated with the sample 
parasitemia (number of parasites per unit volume of blood). Parasitemia levels 
on the order of 10 parasites/microL blood can be unambiguously detected by this 
method. Consideration of laser beam parameters (spot size, rastering across the 
sample surface) and actual sample consumption suggests that the detection limits 
can be further improved by at least an order of magnitude. The influence of 
experimental factors, such as desorbed ion polarity, laser exposure and fluence, 
sample size, and parasite growth stage, on the threshold for parasite detection 
is also addressed.