The rates of penetration, metabolism, and excretion of DDT have been studied in vivo in resistant and susceptible strains of the German cockroach, Blattella germanica (L.). The cockroaches were exposed to various DDT treatments for intervals ranging from 3 to 72 hours. DDT and its metabolites were identified and quantitated in external, internal, and excreta fractions using gas-liquid chromatography. The identifications were verified by thin-layer chromatography. It has been shown that DDT penetration is nearly identical for the three cockroach strains used in this study (two resistant and one susceptible strain). For this reason penetration is not thought to be related to the DDT resistance mechanism in this insect. Susceptible and resistant cockroaches are both capable of converting DDT to dicofol which was the only metabolite observed. The conversion rate is somewhat faster in the resistant strains than in the susceptible strain but in no case exceeds 20% of the absorbed dose. Dicofol production reaches a maximum which is not exceeded in the presence of additional DDT. Female cockroaches of all three strains convert DDT to dicofol at a faster rate than their respective males. The inhibition of dicofol production by the synergist sesamex occurs at a high level in all strains, but results in mortality in the susceptible strain. Therefore, metabolism does not seem to be a major resistance mechanism. Excretion of unchanged DDT is apparently not related to the observed resistance levels. The excretion mechanism is, however, capable of removing much of the penetrated DDT provided the insect can survive the treatment. Excretion of DDT was consistently higher in male cockroaches than in females. The combined effects of the detoxication and excretion mechanisms are extremely efficient in removing penetrated DDT from this insect, particularly at higher treatment levels. Never-the-less, resistant cockroaches have and can apparently withstand much higher internal concentrations of DDT than susceptible cockroaches. The DDT-resistance mechanism of these cockroaches appears to be similar in nature to the unknown mechanism responsible for resistance to knockdown (Kdr) or paralysis by DDT in houseflies. This mechanism may alter the site of action of DDT and result in a reduced binding capacity of resistant insect nerve tissue for the DDT molecule as compared to susceptible insect nerve tissue. / Ph. D.