We have compared the alterations in plasma proteins following treatment of rats with the centrilobular hepatotoxin carbon tetrachloride, the periportal hepatotoxin allyl alcohol and two inducers of hepatic microsomal drug metabolising enzymes, phenobarbitone and a mixture of polychlorinated biphenyls (Aroclor 1254). The results are compared with changes observed in animals treated with agents which caused proliferation of rat liver peroxisomes and described in an earlier publication. Our results indicate that: 1 There is a marked induction of a minor glycoprotein which migrates as a prealbumin following treatment with both inducers of microsomal mixed function oxidases and inducers of peroxisome proliferation. 2 There is a marked increase in a minor α1-glycoprotein when there is chemically-induced mitosis in the liver but not in mitosis following liver damage. 3 Two major α 1-glycoprotein are depressed in all forms of liver damage. 4 There are indications of specific protein responses to allyl alcohol, to inducers of microsomal mixed function oxidases and to inducers of peroxisome proliferation.