Since Castellani's initial work in 1914, investigators of various countries have pointed out the occurrence of human toxoplasmosis, a fact which, still not long ago, was a matter of controversy. As resulting from the works of Torres, Levanditi & coworkers, Wolf, Cowen & Paige, Pinkerton & Henderson and Sabin, the problem of parasitism in man by Toxoplasma has to be faced taking into consideration that there have been described doubtful and undoubtful cases. Doubtful are the cases reported by Castellani (Ceylon, 1914); Fedorovitch (The Black Sea, 1916); Chalmers & Kamar (Sudan, 1920); and Bland (London, 1930-31). Undoubtful are those reported by Janku (Praga, 1923); Torres (Rio de Janeiro, 1927); Wolf & Cowen (New York, 1937); Richter (Chicago, 1936: diagnosed by Wolf & Cowen in 1938); Wolf, Cowen & Paige (New York, 1939); Hertig (Massachusetts, 1935: diagnosed by Pinkerton & Weinman in 1940); Pinkerton & Weinman (Lima, Peru, 1940); Sabin (2 cases, Cincinnati, 1941); Pinkerton & Henderson (2 cases, Saint Louis, 1941); Paige, Cowen & Wolf (3 cases, New York, 1942); and De Lange (Amsterdam, 1929: diagnosed by Paige, Cowen & Wolf in 1942) .Of these reports considered as undoubtful cases of human toxoplasmosis, 10 represent congenital disease (Torres and Paige, Wolf & Cowen), having occurred in either new born or a-few-month-old children. As in the cases, in which it was possible to examine the mothers of those children, these women were of a healthy appearance, the conclusion was drawn that the disease, although extremely severe and fatal, can present an unapparent form. In 2 cases, serum protection tests proved such an unapparent infection of the mothers, in whom neutralizing antibodies against Toxoplasma were met with (Paige, Cowen & Wolf). Although no detailed microscopical study has been made in all cases, the disease is characterized by granulomatous meningoencephalomyelitis (Wolf & Cowen), often associated with myocarditis and chorioretinitis. The symptoms presented by the patients were: fever, convulsions, respiratory disturbances, hydrocephalus, cyanosis, vomiting, temperature lability, etc., the diagnostic sign of the greatest importance being the presence of foci of profound cerebral calcification and chorioretinitis in new born (Wolf, Cowen & Paige). In 2 cases of toxoplasmosis verified in one 6 and the other 8 years old, patients, an encephalitis, clinically atypical, was met with, one of them having recovered his health (Sabin). The remaining three cases were described in adults; in one of them the changes were not typical (these was a concomittant infection by Bartonella bacilliformis) and in the two others the disease assumed an "exanthematous form", simulating a macular fever (Pinkerton & Henderson), the most important microscopical evidence being an interstitial pneumonia. Apart from the clinical similarity, also the encephalitis foci met with in this "exanthematous form" of toxoplasmosis resemble those described in "macular fevers"…