Experience in the WHO field programme for evaluating the safety of new insecticides.

After careful laboratory evaluation every new insecticide is subjected to village-scale trials, under the WHO Scheme for Evaluating and Testing New Insecticides, before it can be recommended for general use. Several such trials have been conducted to obtain both entomological and toxicological information. The toxicological assessment includes both clinical observations and laboratory tests on both spray-men and residents.Laboratory tests should be of a kind suitable for field operations. So far only serum cholinesterase determinations have proved suitable: determinations are usually made before spraying, immediately after spraying, and again a few weeks later.THE FINAL EVALUATION OF THE SAFETY OF A NEW INSECTICIDE MUST ALWAYS TAKE INTO ACCOUNT THE CONDITIONS UNDER WHICH IT IS LIKELY TO BE USED: it must be remembered that it will be used in confined spaces, that it may contaminate bedding and food, that safety precautions by the spray-men will be negligible, and that the general supervision will be inadequate.