The hematological parameters were assayed in Plasmodium vivax patients with only one infection, two infections, three infections and more than three malarial infections during a period of six months. A steady fall in the levels of hemoglobin as well as packed cell volume (PCV) level was observed with increasing number of infections. The malarial patients showed a progressive decrease in RBC level with increasing number of attacks. The decrease in the hematological indices was statistically significant at all levels of parasitemia. There was a marked increase in the osmotic fragility of the malarial erythrocytes when compared to that of controls. During repeated malarial attacks, significant decrease in MCH (p<0.05) and MCHC (p<0.01) and increase in the MCV level (p <0.05) and Heinz body formation (p<0.001) were observed. Parasite density significantly influenced the fragility of the erythrocytes, Heinz body formation, MCV, MCH and MCHC levels. Thus, the erythrocytes of the patients repeatedly infected with Plasmodium vivax parasite are subjected to structural and functional impairment, ultimately culminating in anemia.