An object of this invention is to provide a method for assaying,
predicting or assessing drug metabolism by effectively detecting (a)
mutation(s) in a gene coding for UGT. A gene coding for UGT comprises 5
exons, and since the regions of exons 2 through 5 are common to each
isoform of UGT1, by assaying a mutation in the common regions,
particularly a mutation in exon 5 region, and further adding the
detection of (a) mutation(s) in a plurality of exon regions, mutations of
UGT1 gene can effectively assayed. A nucleic acid chip using nucleic acid
probes is used as a way of detecting (a) mutation(s).