Steroids and steroid-related enzymes producing biologically active metabolites are vital for human physiology. Our research is focused on enzymatic processes, regulation and cellular actions involving vitamin D and other steroids. We study e g vitamin D metabolism and the mechanisms whereby active vitamin D act on eukaryotic cells. Altered vitamin D levels in plasma are linked to a number of disease conditions. It is therefore important to obtain more knowledge about the metabolism and effects of vitamin D and related compounds. The biologically active form of vitamin D, 1a,25-dihydroxyvitamin D3, blocks cell division and increases cell differentiation. Vitamin D analogues (synthetic compounds with vitamin D-like effects) are used in treatment of psoriasis and are of interest in development of new cancer therapies. Our studies include effects of vitamin D analogues on glioblastoma, an incurable type of brain cancer. Other steroids of interest in our investigations are oxysterols (cholesterol derivatives) and sex hormones and their actions in the central nervous system.