The use of chlorinated hydrocarbon pesticides for the control of tropical diseases and the treatment of agricultural crops in Central Africa has [ncreased tremendously since it was started in 1954 (LAMBRECHT, 1954; BRION, 1962). Even though the levels of residues from such pesticides have been studied extensively in many parts of the world, there are few data frorn this region (KOEMAN and PENNINGS, 1970; EVERAARTS, et al., 1971; KOEMAN, et al., 1971, 197Z). The purpose of this study was to determine the level of pesticides over a period of time in the fish in the northern portion of Lake Tanganyika which are used as a source of prote[n by the surrounding populations. Lake Tanganyika should make an excellent study area since it[s almost a closed system and is surrounded by cotton plantations, especially at the northern end. AREA AND SCOPE OF STUDY Lake Tanganyika, s[tuated in the Rift Valley of Africa, is 650 km long and up to 70 km wide(see Figure 1). The surface is approximately 800 m above sea level and the lake has a maximum depth of 1500 m and an estimated volume of 30, 000 km 3. The annual rainfall of approximately 1 m and river inflow from the Ruzizi and Malagarasi rivers could raise the level by 0.5 m per year except for loss by evaporation (95 %) and drainage into the Lukuga river (5 %). This small drainage makes the lake similar to many closed systems. The wet season in the northern part of the lake starts near the first of October and the dry season near the 20th of May. The water chemistry of the lake is described by several authors (BEAUCHAMP, 1940, 1964; KUFFERATH, 1952; CAPART, 1952; TALLING and TALLING, 1965; DEGEN, et al., 1971). During the cotton season of 1971-72 (primarily in May), the cotton fields in Burundi at the northern end of the lake were