The observations made during the year from September, 1932, to August, 1933, on the malaria rates among the inhabitants of five villages in the mid-basin of the Chagres River in Panama are summarized. With regard to the parasite rate, a notable decrease occurred during the late fall and early winter months of 1932, followed by a sudden rise in January, 1933, to a relatively high rate, which persisted to the end of the period. The proportions of the three types of parasite during the preceding year and in the year under consideration are given, showing that estivoautumnal malaria, the most common, increased slightly during the last year, forming 89.2 per cent of all malaria found. Crescent incidence showed a very small variation from month to month, averaging 29.2 per cent for the period. A rate of 20.7 per cent was found in a small number of infants examined. The incidence of clinical malaria, intensity of infection, immunity, and associated phenomena are discussed. The high annual parasite rate of 803 per thousand was found in persons examined 12 times at monthly intervals throughout the period.