Novel diphosphonate homologs7a–7c,and their cyclic counterparts8a–8c,of the previously synthesized farnesyl pyrophosphate analogs1and2were prepared and tested for their inhibition potency and specificity of the enzymes PFT and PGGT-I. Compound2was shown to be the most potent inhibitor of PFT (IC 50 = 0.58 ± 0.45 μM) in this series. The novel compound7a,the one carbon homolog of2,proved to be the most potent inhibitor of PGGT-I (IC 50 = 0.98 ± 0.01 μM). The cyclic analogs8a–8care generally less biologically active. The compounds2and7aare nonspecific toward inhibition of PFT and PGGT-I and may inhibit both farnesylation and geranylgeranylation processing of oncogenic proteins.