AbstractThe activities of natural and synthetic pyrethroids against male German cockroaches (Blattella germanica)were examined by means of dusting and direct spraying techniques. NRDC 107 (5‐benzyl‐3‐furylmethyl(+)‐trans‐chrysanthemate) was the most active compound in killing cockroaches. Pyrethrins gave the most rapid knockdown and were 60% as active as NRDC 107 (Bioresmethrin) in killing power. Tetramethrin and the corresponding(+)‐trans‐ester gave rapid knockdown. Only(+)‐trans‐allethrin[(+)‐trans‐chrysan‐themate of(±)‐allethrolone] provided useful knockdown and killing power together. Piperonyl butoxide had a relatively stronger synergistic action with less active killing agents. The rate of knockdown during the first few minutes of exposure was not altered gre