The diphosphate moiety of geranylgeranyldiphosphate (GGdP) was replaced with metabolically and hydrolytically stable analogous polar portions, in an attempt to obtain new geranylgeranyltransferase (GGTase) inhibitors, which could also be selective over congener enzyme farnesyltransferase (FTase). In particular, the phosphonomethylphosphorylmethoxy derivative showed the highest inhibition potency, accompanied by a satisfactory GGTase/FTase selectivity.