Undecaprenyl pyrophosphate synthetase and geranylgeranyl pyrophosphate synthetase were partially purified and characterized from Bacillus subtilis, from which heptaprenyl pyrophosphate synthetase and farnesyl pyrophosphate synthetase had previously been obtained [Takahashi et al. (1980) J. Biol. Chem. 255, 4539; (1981) J. Biochem. 89, 1581]. The undecaprenyl pyrophosphate synthetase catalyzed the Z-oligomerization of isopentenyl units with farnesyl pyrophosphate as a priming substrate to give C50 and C55 prenyl pyrophosphates with Z,E mixed stereochemistry. Various geometric isomers of C10, C15, C20, and C25 prenyl pyrophosphates also acted as priming substrates to give the corresponding isomeric products with chain lengths of C50 and C55, including unnatural products. In addition to absolute requirements for Mg2+ and detergent, the enzyme activity was further stimulated markedly by monovalent cations such as K- and NH4+. The geranylgeranyl pyrophosphate synthetase catalyzed C5 leads to C10 leads to C15 leads to C20 reactions to give E,E-farnesyl and E,E,E-geranylgeranyl pyrophosphates. This enzyme was not affected by monovalent cations or detergent.