The thin blood films are essential for study of morphology and identification of blood parasites specially species of Plasmodium. In case of low number of malarial parasites thick blood film is required. For the success of management of Plasmodium falciparum malaria the assessment of parasite density or pasitemia is significant. A formula has been evolved for the assessment of parasite density. The procedure of counting of parasites in proportion of WBC and RBC based on that formula has been described in this chapter.