Microscopic examination Two thick and thin blood films for parasite counts and species identification will be obtained as shown in table 3 and whenever a child returns to the Bandim health centre. Slides will be stained using freshly prepared Giemsa and examined with 1000 x magnification. The number of asexual parasites per 200 white blood cells will be counted or, if parasitaemia is high, the number of white blood cells per 500 parasites will be counted. Parasite density will be assessed independently by 2 qualified microscopists. Discordant results will be read a third time.