In a previous report we described the transmission of the malaria parasites by the oral route in a murine model. Later, we performed some experiments to demonstrate the transmission of malaria infection by cannibalism. Now we commence to look for the site, mechanism and stages of the parasite involved in crossing the alimentary canal to reach blood and start the infection. To know the invasive stage of the parasite and the way it penetrates, we wanted first to find the level of the digestive tract through which the parasites cross, to restrict the area to be studied. We proposed that the crossing place would be known, if the crossing time of the parasite could be established. Mice were orally inoculated with Plasmodium yoelii yoelii infected blood and their blood was transferred at different times into clean recipient mice intraperitoneally. Malaria infection detected in recipient mice proved that infective forms of the parasite were circulating in the donor mice at the time the blood samples were taken. In this way, we observed that: i) although most parasites required between 2 to 10 min for crossing the alimentary canal, in some case the process can last for 22 hrs; ii) the parasites circulate in blood for variable periods of time (only two minutes in the shortest, and from 10 min on in the longest) being infective to blood recipients. Most orally-inoculated mice whose blood infects other mice, became transient carriers of parasites unable to establish in them.