(1)A study of the blood picture was made of 147 Puerto Rican young men who had no clinical symptoms but in whom the infection with Schistosoma mansoni as well as other intestinal parasites such as Hookworm, Trichocephalus trichiurus, Strongyloides stercoralis and Ascaris lumbricoides were found on routine fecal examination.
(2)There were 17 individuals infected with S. mansoni alone. In this group 5 had leukocytosis and 6 had eosinophilia. The highest count was 14 per cent and there were 3 persons who had no eosinophiles.
(3)The only alterations from normal in the remainder of the group were increases of varying degree of the percentages of eosinophiles and slight leukocytosis. The highest eosinophilia was 30 per cent. The highest counts being in those in whom there were S. mansoni, Hookworm, and T. trichiurus. There were 17 individuals of the 147 studied in whom no eosinophiles were found.
(4)In spite of the various parasitic infections present in the group of 147 young men, the blood picture shows a striking resemblance to the blood findings in 450 healthy Puerto Rican males who were free from intestinal and blood parasites.