A novel mRNA species is specified by the Q6/Q8 gene, a member of the Qa-2-determining family of class-I genes of the murine major histocompatibility complex. It is longer than all previously described class-I transcripts due to an extension at the 3' end of the mRNA past the predicted polyadenylation site. This mRNA was detected by Northern-blot analyses with single or low-copy-number probes to the 3' end of the Q6/Q8 gene. RNase protection experiments have confirmed this finding. The appearance of this mRNA in different strains of mice correlates with the synthesis of the Qa-2 molecule.