In the cases of naturally induced falciparum malaria which have come under our observation, the days elapsing from inoculation to the first detection of parasites have varied from 6 to 25 (1), in this respect showing a slightly greater range than has been noted with vivax malaria (8 to 23). Since in a previous paper (2) we have examined certain factors which might conceivably influence the duration of this period in vivax malaria, it appeared desirable to analyze similarly our observations on this feature in infections with the falciparum parasite. The data considered relate to 96 successful inoculations made by mosquitoes from 34 lots of infected A. quadrimaculatus. These involved five strains of this parasite, all of local autochthonous origin, of which the strains designated as Coker and Long have been most extensively employed. In the subsequent analyses these are separately presented.