The effects of 1,25-VD on the mRNA expression levels of HIST1H1C, HFE, SGCZ, TUSC3, and CYP24A1 (cytochrome P450 family 24 subfamily A member 1), a well-known 1,25-VD target gene, were examined using quantitative real-time polymerase chain reaction (qRT-PCR) in PC-3 human prostate cancer cells. The gene discussed is CYP24A1; the disease is prostate cancer.