The examination of 9,950 serums in Guadeloupe and Martinique has revealed the importance and the precocity of infestation by Toxoplasma: 56,9% of the population has complement fixing antibodies, 65,6% haemagglutinating antibodies and from the very first age groups onwards, nearly half the population is found to be infested. Although the consumption of insufficiently cooked meat is most frequently invoked, it would seem that this manner of contamination should not be incriminated in Guadeloupe and Martinique where the population traditionally lives on fish and well-cooked meat. Moreover, the great variability in the rates of infestation observed in the different localities studied leads one to envisage the invtervention of climatic factors favoring the survival of the oocysts born of the sexed multipilication of the parasite in the external environment.