A method has been devised for observing the effects of a number of non‐volatile contact poisons on the oxygen uptake of groups ofOryzaephilus surinamensis.Toxic concentrations of D.D.T. and of its analogues applied as dusts toO. surinamensisincrease the rate of oxygen uptake: sublethal concentrations appear to have no effect. The total oxygen uptake of groups of starvingO. surinamensisappears to be constant, whether or not they are treated with D.D.T. or its analogues. In each case a linear relationship appears between length of life and total volume respired before death.The stimulus of D.D.T. toO. surinamensisis apparently quantal and the magnitude is independent of the concentration of D.D.T. in the dust. The stimuli resulting from the action of D.D.T. and its analogues are approximately equal, as are the rates at which the insects die. There is, however, apparently a correlation between molecular weight and length of life, i.e. there is a tendency for the insects treated with the poisons of lower molecular weight to die more rapidly than those treated with the analogues of high molecular weight.The effect of benzene hexachloride on the respiration ofO. surinamensishas been shown to be similar to that of D.D.T.The effects of a number of insecticides on the oxygen uptake ofO. surinamensishave been compared. As a result the insecticides have been classified in two groups:(a)those stimulating respiration, e.g. D.D.T., B.H.C., pyrethrins;(b)those depressing respiration, e.g. rotenone, Lethane B 7