(VDR)relativetoABL1transcript,andflowcytometrytostudythe apoptotic effect of VD. VD induced apoptosis of cultured lymphocytes in P prior to remission, but not in C or in P at relapse (Fig 1B, C). Response to VD correlated with VDR expression (Fig 1C). Pepper et al (2003) demonstrated that lymphocytes from CLL patients overexpress variable levels of VDR, and that an analog of 1-25(OH) 2 D 3 , can induce apoptosis of these cells in vitro. Our observations strongly suggest that these in vitro concepts may hold true in vivo, with VD supplementation at the conventional dose. This effect seems to be related to the level of VDR expression in lymphocytes. It could be speculated that patients with higher VDR levels could have the best response to VD therapy. Our late observations in P also suggest that VD resistance may also develop. A clinical trial is now needed to determine whether there is room for VD in the treatment of CLL.