Megakaryocytopoiesis was selectively inhibited in cultured murine bone marrow cells by a 15-mer oligodeoxynucleotide complementary to the initiator AUG region in butyrylcholinesterase mRNA. Furthermore, conditioned medium from Xenopus oocytes producing recombinant butyrylcholinesterase stimulated megakaryocytopoiesis. These observations implicate butyrylcholinesterase in megakaryocytopoiesis and suggest application of oligodeoxynucleotides for modulating bone marrow development.