Transformation of ten colchicinoids by isolated rat liver microsomes resulted in the mixture of C-2, C-3, and C-10 O-demethylated metabolites. Colchicinoids administered i.p. to rats (2.5 mumol/kg) increased serum and liver activities of alkaline phosphatase and decreased liver microsomal demethylase activity as well as cytochrome P-450 content. The changes of acid phosphatase level were less pronounced. The aspartate and alanine aminotransferase activities were significantly increased only in colchicine treated rats. No relations between enzyme activity changes and colchicinoid hydrophobicities quantified by partition coefficients (log P) were found. However, the enzyme activity changes were related to the type of substitution at C-3, C-7, and C-10 of colchicinoids. Particularly, O-demethylation at C-3 resulted into the fall of alkaline phosphatase response. On the other hand, the microsomal demethylation and cytochrome P-450 content were related to the modification of the nitrogen substituent at C-7.