3-isobutyl-1-methylxanthine (IBMX) is a nonselective inhibitor of cAMP and cGMP phosphodiesterases (PDEs). Research studies show that IBMX inhibits many members of the PDE family, with the exceptions of PDE8A, PDE8B, and PDE9 (1-4). Treatment of cells with IBMX promotes accumulation of cAMP and cGMP, which leads to activation of cyclic- nucleotide- regulated protein kinases (5,6). Additional research indicates that IBMX can promote neuronal progenitor cell maturation in vitro (7).