In a trial carried out in 1958, aldrin applied as a fog with a swingfog machine at concentrations of 10 and 20 per cent in gas oil was more effective than dieldrin or chlordane at similar concentrations for control of Atta cephalotes. Two applications of 10 and 20 per cent benzene hexachloride and toxaphene failed to give complete control. In a subsequent trial, aldrin in concentrations ranging from 2·5 to 8·0 per cent was also found to be effective against A. cephalotes but against A. laevigata, aldrin and dieldrin were more effective than chlordane at concentrations of 5·0 and 2·5 per cent. In campaigns carried out from 1959 to 1963, 5000 nests were destroyed by fogging with 2·5 per cent aldrin in gas oil.