We amplified by PCR and characterized a fragment of cDNA from rat spleen, encoding the distinctive C-terminal region of the acetylcholinesterase (AChE) H subunit. A recombinant vector encoding this subunit was constructed and expressed in COS cells: the H subunits produced glycophosphatidylinositol (GPI)-anchored dimers, showing that the spleen cDNA fragment contained a functional GPI cleavage/attachment site. Using PCR, we did not detect mRNAs encoding AChE H in rat muscle or hypothalamus. In the liver of 16-day rat embryos, we found both H and T transcripts, in agreement with the presence of both GPI-anchored dimers and amphiphilic monomers of type II. In addition, we detected 'read-through' (R) transcripts, in which regular introns are spliced, but the intervening sequence between the common exon 4 and the alternative exon 5 (H) is maintained.