Steroids and steroid-related genes and enzymes, producing biologically active metabolites, are vital for human physiology. Our research is focused on the properties and regulation of enzymatic processes involving steroids, including vitamin D. We study enzymes and genes of importance for vitamin D bioactivation, metabolism and function as well as the effects of active vitamin D and similar compounds on eukaryotic cells. Many drugs result in adverse side effects, including increased risk of bone disease. We study the mechanisms by which anti-inflammatory, anti-viral and anti-epileptic drugs affect cells, with particular focus on vitamin D-related function in the bone and the central nervous system. Vitamin D is needed for regulation of calcium levels in the body and vitamin D deficiency leads to skeletal diseases such as rickets in children and osteomalacia/osteoporosis in adults. The biologically active form of vitamin D, 1alpha,25-dihydroxyvitamin D3, formed through metabolic activation, 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 therapy. Our studies include effects of newly synthesized vitamin D analogues on glioblastoma, an incurable type of brain cancer. Altered vitamin D levels in plasma are linked to a number of different conditions including neuropsychiatric and neurodegenerative disease. For these reasons, it is important to obtain more knowledge about activation and metabolism of vitamin D and the roles of the formed metabolites. Other steroids of interest in our investigations are oxysterols (cholesterol derivatives) and sex hormones including estrogens. Studies on these steroids particularly focus on cells of the central nervous system, where effects of neuroactive steroids are insufficiently characterized but believed to be of importance in a wide range of normal and disease conditions.