1.Studies in certain areas within the low, coastal region of the State of Rio de Janeiro, Brazil, have revealed a very small number of infections with Plasmodium malariae. Reasons are given for believing that some infections have been missed and others wrongly diagnosed at the time of the surveys.
2.The data indicate that the quartan rate probably fluctuates in the same manner as that of the other malaria infections. The persistence of P. malariae blood infections during months of low fever incidence has been verified.
3.The geographical distribution of the P. malariae infections reveals the presence of definite foci which consistently produce new cases each year. There is no obvious reason why the rate should continue so low, i.e., why there is no epidemic increase in quartan comparable to that of the other malaria fevers.