Measurement of parasite growth inhibition by microscopy and flow cytometry. Correlation between duplicate wells of parasitaemia counts from a growth inhibition assay using (A) ring stage microscopy (n = 70) or (B) flow cytometry (n = 55). The higher number of samples available for ring stage microscopy reflects the availability of counts from a second microscopist. The PfMSP1-19 line was used in this comparison and tested for inhibition by rabbit anti-MSP1-19 antibodies and a selection of samples from malaria-exposed and non-exposed donors. (C) Mean parasitaemia counts for duplicate wells determined by ring stage microscopy counts for microscopist one (M1) and microscopist two (M2) compared to parasitaemia measured by flow cytometry (trophozoite stage parasites) using the PcMSP1-19 and PfMSP1-19 lines. Samples used were serum from malaria exposed individuals and unexposed controls numbered 1-26 for ease of comparison.