The active hormonal form of vitamin D, 1α,25-dihydroxyvitamin D3, is reported to have 1000s of biological targets. The growth-suppressive properties of 1α,25-dihydroxyvitamin D3and its synthetic analogs have attracted interest for the development of treatment and/or prevention of cancer. We examined effects of 1α,25-dihydroxyvitamin D3and the vitamin D analog tacalcitol on signaling pathways and anchorage-independent growth in T98G and U251 glioblastoma cells. Assay of signaling proteins important for cellular growth indicated suppression of p70-S6 kinase levels by 1α,25-dihydroxyvitamin D3and tacalcitol in T98G cells, whereas the levels of PLCγ, a target for phospholipid signaling, was slightly increased.