The hostile environment of the mosquito gut by penetrating the midgut epithelium. Underneath the basal lamina, the ookinete differentiates into an oocyst which reproduces asexually to form sporozoites. These are released into the haemocoel and migrate to and invade the salivary glands. During development in the mosquito, Plasmodium passes through several bottlenecks of which the transition from ookinete to oocyst accounts for the greatest loss in parasite numbers. The major immunity factor thioester-containing protein 1 together with the two leucine-rich proteins, leucine-rich repeat immune protein 1 and Anopheles Plasmodium-responsive leucinerich repeat 1 are mosquito innate immunity effectors that are mainly responsible for the losses at this stage. Significant parasite loss also occurs during the following stage where ‘midgut sporozoites’ are released from the oocysts into the haemocoel and colonise the salivary glands although the mechanisms and effector molecules that invoke such losses remain obscure. Only,20% of mgs have been shown to invade salivary glands. Although phagocytosis of sporozoites in the haemocoel has been reported in Anopheles and Aedes mosquitoes, the fraction of sporozoites eliminated by phagocytosis is small despite the capability of haemocytes to phagocytose large number of foreign particles or bacteria. Some of the sporozoites erroneously locate and become trapped in distal extremities irrelevant for the transmission cycle such as wings or legs. At the molecular level, however the precise mechanism of reduction by SRPN6 remains to be uncovered. As sgs are responsible for the establishment of an infection in the vertebrate host, new methods are needed to dissect mechanisms that affect sgs numbers in the mosquitoes. A series of methods have been developed which vary in accuracy, sensitivity and simplicity, nevertheless quantification of Plasmodium loads in mosquitoes remains a laborious and time consuming task. Either direct observation and counting of parasite forms or quantification of parasite components have been employed but all suffer from significant technical difficulties. Here, we report the development of a biochemical assay to evaluate parasite loads in salivary glands of infected mosquitoes that avoids dissection of salivary glands and isolation of sporozoites. The assay uses transgenic P. AG-013736 berghei designed to express a reporter gene exclusively in sgs and not mgs. Mining the results of a subtractive hybridisation screen for genes that expressed in P. berghei mgs or sgs and proteome analyses of P. falciparum mgs or sgs led to a choice of three promoters to drive expression of the reporter gene: upregulated in infective sporozoites 3, uis10 and glyceraldehyde-3-phospho-dehydrogenase. P. berghei expressing a fusion protein of GFP and luciferase have been used to detect blood and liver stages of the parasite as well as to visualise infection in dissected organs or whole bodies of mice. Luciferase activity of such reporter lines has been previously exploited for screening of antimalarial drugs. We chose gfp-luc as a fusion reporter gene enabling parasite detection by fluorescence microscopy and enzymatic activity measurement of luciferase in the transgenic lines. We generated and characterised two salivary gland-specific reporter P. berghei lines and established a simple biochemical assay to examine sgs loads.