Reciprocal crosses were made between a DDT-resistant and a nonresistant strain of the German cockroach.

The techniques employed in rearing the roaches and obtaining toxicological data on the different strains, as well as the genetical and statistical procedures, are described.

The toxicological data are presented in the form of regression lines with appropriate statistical analyses.

A table showing the relative resistance to DDT of the various strains involved in this study is included.

Several conclusions are drawn relative to the inheritance of resistance to DDF in the German cockroach.