AbstractThe knockdown and contact killing actions of various pyrethroids were compared usingBlattella germanicaandPeriplaneta americana. A wide range of knockdown activity was found; 5‐benzyl‐3‐furylmethyl (1R)‐cis‐3‐(dihydro‐2‐oxo‐3‐thienylidenemethyl)‐2,2‐dimethylcyclopropanecarboxylate (RU 15525) acted fastest, more rapidly than pyrethrins, againstB. germanicaas well as having a low LD50value. Topical application and direct spray tests showed that (S)‐α‐cyano‐3‐phenoxybenzyl (1R)‐cir‐3‐(2,2‐dibromovinyl)‐2,2‐dimethylcyclopropanecarboxylate (NRDC 161) was more active as a killing agent, by an order of magnitude, than cismethrin, the next most active compound, and also had considerable knockdown activity. Piperonyl butoxide generally had little synergist effect. FemaleP. americanawere over three times more tolerant than males to a range of insecticides applied topically. Residual knockdown action in the WHO resistance test was observed to provide baseline data. There was little overlap in speed of action between pyrethroids and o