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Orally administered 3,4-dichloroaniline is absorbed by the body, metabolized in the liver and excreted mainly via urine. A low dose of 3,4-dichloroaniline (approx. 5 µg) was excreted to about 80 % within 24 h and completely excreted within 72 h by rats, without any bioaccumulation in tissues (Worobey and Shields, 1991). Oral as well as dermal administration of a higher dose of 3,4-dichloroaniline (12 mg) instead led to an increased excretion of parent compound (indicating saturation of the biotransformation pathways) and a total excretion of only 2 % of the administered dose within 24 h (El Marbouh et al., 2002). The main metabolite detected in urine of male rats was 2-amino-4,5-dichlorophenol. In vitro rat liver microsomes metabolized 3,4-dichloroaniline in the presence of NADPH-regenerating system (indicating the involvement of CYP450 -Phase I enzymes) to the two main metabolites N-hydroxy- and 6-hydroxy-3,4 -dichloroaniline with apparent km-values of 0.12 mM and 0.29 mM, respectively (McMillan, 1990a). Pretreatment of rats with 3,4-dichloraniline (100 mg/ kg, 3 d, i.p.) increased NADPH-dependent metabolite formation in rats by about two-fold (Mc Millan, 1990b). 3,4-dichloroaniline therefore is a weak inducer of microsomal enzymes. 3,4-dichloroaniline metabolism in male rabbit microsomes resembles that in rats. N-hydroxy- and 6-hydroxy-3,4-dichloroaniline are the main metabolites, with N-hydroxy-3,4-dichloroaniline being able to induce methemoglobin formation (Lenk and Sterzl, 1978). Very little dermal absorption through intact skin was observed within the first 4 h of application (Levillain, 1998). Nevertheless the choice of solvent (emulsifier) and the condition of the skin (lesion) can enhance the amount of 3,4-dichloroaniline that is absorbed through the skin (Marty, 1979).