Prenylation or isoprenylation is the addition of hydrophobic molecules to a protein to facilitate its attachment to the cell membrane. The result is similar to that of all lipid anchored proteins (e.g. the GPI anchor). All isoprenylation chains are products of the HMG-CoA reductase pathway: geranylgeraniol (GG), farnesol and dolichol.

Proteins that undergo prenylation include ras, which plays a central role in the development of cancer. This suggests that inhibitors of prenylation enzymes (e.g. farnesyltransferase) may influence tumor growth.