AbstractMarmosets were given either a hepatotoxin, carbon tetrachloride, orally or an i.m. injection of a mytoxin, chlorpromazine. Although muscle damage alone caused small increases in the plasma levels of lactate dehydrogenase, alanine aminotransferase, aspartate aminotransferase and isocitrate dehydrogenase (ICDH), only the isoenzyme analysis of ICDH can differentiate definitely between liver and muscle damage. Only very severe muscle damage can increase the plasma concentration of this enzyme but, in this case, the elevation of plasma creatinine kinase levels helps differentiation. It is recommended that the elevation of ICDH is the most specific indicator of hepatic damage in the marmoset.