It is the aim of this document to take the ecotoxicologist's point of view and consider effects on populations of organisms in the environment. The risk to human health of the use of DDT was evaluated in Environmental Health Criteria 9: DDT and its Derivatives (WHO, 1979). This document did not consider effects on organisms in the environment, but did consider environmental levels of DDT likely to arise from recommended uses. No attempt has been made here to reassess the human health risk; the interested reader should refer to the original document, which contains the relevant literature in this area. This document, although based on a thorough survey of the literature, is not intended to be exhaustive in the material included. In order to keep the document concise, only those data which were considered to be essential in the evaluation of the risk posed by DDT to the environment have been included. Biomagnification refers, in this document, to the progressive accumulation of chemicals along a food chain.