We report the characterization of a novel human gamma-glutamyltransferase mRNA type. This type III mRNA differs from type I and type II mRNAs previously described by several point mutations and the presence of an unspliced 81 bp intron in the open reading frame. Further, type III mRNAs are truncated ones and are tissue and pathology specifically expressed. In fact, type III mRNAs are present in human placenta, sigmoid, lung and in 50% of acute lymphoblastic leukemia blood cells but they are never found in healthy lymphocytes.