The authors describe a series of experiments designed to determine the extent to which cross-resistance exists in insecticide-resistant strains of the German cockroach. The tests were conducted by exposing females from a DDT-resistant strain, a chlordane-resistant strain, and a non-resistant strain to varying concentrations of several insecticides. From these tests mortality data were obtained and are presented in the form of regression lines.The insecticides used were DDT, methoxychlor, chlordane, dieldrin, Prolan, malathion, allethrin, and Lethane; these were chosen so that a wide variety of chemical types would be represented.The results indicate that the DDT-resistant strain is highly resistant to DDT and to its analogue, methoxychlor, but not to any of the other insecticides tested. Similarly, the chlordane-resistant strain is highly resistant to chlordane and to its analogue, dieldrin, but is susceptible to the other toxicants listed.From these results, as well as those obtained by others, it appears that the picture of cross-resistance in the German cockroach is in essential agreement with that which is emerging for other insects throughout the world.