We found that there are at least five subclasses of N-acetylglucosaminyltransferase I (GnT-I; EC 2.4.1.101) mRNA with different 5′-untranslated regions in rat brain. These five subclasses were also expressed in many tissues with distinct tissue-specific patterns. Moreover, they were regulated differently in response to acute-phase inflammation. The expression of the most abundant subclass of GnT-I mRNA in rat liver decreased 2.5-fold in response to inflammation, concomitantly with a significant decrease in the total amount of GnT-I mRNA. In contrast, one of the minor subclasses of GnT-I mRNA was induced 10-fold by inflammation.