SUMMARY.1. The first part of this paper forms a general introduction to investigations carried out on contact insecticides. The methods used are briefly described and some consideration is given to the mode of expressing results.2. The second part deals in detail with the insecticidal properties ofTephrosia VogeliiHook. which, with other species of this genus, occurs abundantly in many parts of the world. The aqueous and alcoholic extracts of the leaves and seeds ofT. Vogeliiare shown to be highly toxic toAphis rumicisL., the toxicity being of the same order as that of nicotine. Extracts of the stems have not proved so poisonous.3. The plants of the genusTephrosiaseem to offer possibilities for practical use as insecticides and it is hoped to extend the work in this direction.