Dihydrotanshinone I (DI) is a naturally occurring compound extracted from Salvia miltiorrhiza Bunge, also known as Chinese sage, red sage root, and the Chinese herbal Dan Shen. It belongs to a class of lipophilic abietane biterpenoids and has been reported to have cytotoxicity to a variety of tumor cells. Since they were first discovered, over 40 related compounds and over 50 hydrophilic compounds have been isolated from Dan Shen. Trans-R was found to be the most potent antiproliferative agent. Cis-R demonstrated somewhat less potency compared to trans-R. Unlike cis-R and trans-R, dihydro-R exhibits moderate proliferative effect on androgen-independent prostate cancer cell lines PC-3 and DU-145 at picomolar concentrations. At higher concentrations, dihydro-R caused proliferation inhibition, similar to cis-R and trans-R.