AT THE PRESENT TIME there is no accepted serological test which is adaptable to routine use in the investigation of the production of antibody in malarial infections. Attempts in the past to obtain specific complement-fixation and precipitation reactions with sera from patients infected with malaria have met with limited success.1,2 The fluorescent-antibody technique has been successfully used in the specific staining of malarial parasites,3,4and our investigations were undertaken using the indirect method of immunofluorescence5to follow the course of production of antibody in normal volunteers infected byPlasmodium vivaxand the simian parasite, the B strain ofP cynomolgi. The suggestion that a humoral element of malarial immunity is produced in natural infections and is gamma globulin has been expressed by several investigators.6-9We were therefore also interested in determining whether any relationship exists between changes in serum gamma globulin and the production of