Male and female Sprague‐Dawley rats were treated once with either crude or purified hexachlorobenzene (HCB) or crude or purified hexabromobenzene (HBB) at 150 mg/kg, intraperitoneally. Examination of hepatic microsomes 4 d later revealed an increase in cytochrome P‐450 levels in both HCB‐ and HBB‐pretreated animals. HBB produced a slight but statistically significant hypsochromic shift. Both HCB and HBB produced an increase in benzphetamine N‐dealkylation: HCB produced a greater effect than HBB, and male rat microsomes produced more HCHO than female rat microsomes from the N‐demethylation of benzphetamine. HCB and HBB both enhanced ethoxycoumarin and ethoxyresorufin O‐dealkylation. Liver‐to‐body weight ratios were not significantly affected by pretreatment with either halogenated compound. There appeared to be no difference between the crude and purified halogenated compounds. Electrophoresis of microsomes from male rats pretreated with purified HBB indicated the presence of a band at 53,000 daltons, which was also seen in microsomes from rats pretreated with 3‐methylchotanthrene. This band was absent in microsomes from rats pretreated with phenobarbital. Evidence from other laboratories has demonstrated the mixed type of P‐450(s) induction after HCB administration, as does this report using enzymic and electrophoretic data.