Active vitamin D metabolites are not only involved in the regulation of bone metabolism but exerts immunomodulatory effects important in the regulation of inflammatory processes. The purpose of the present study was to evaluate the effects of a short-time treatment with 1 alpha-hydroxycholecalciferol on both disease activity and bone metabolism in patients with rheumatoid arthritis (RA). The effects of an adjuvant therapy with 1 microgram 1 alpha-hydroxycholecalciferol over eight weeks on conventional parameters of disease activity (Ritchie index, duration of morning stiffness, C-reactive protein, ESR), serum levels of cytokines and soluble cytokine receptors (TNF-alpha, IL-6, IL-4, sIL-2R, sIL-6R) and parameters of bone metabolism (bone-specific alkaline phosphatase, osteocalcin, renal excretion of pyridinolin- and desoxypyridinolin-collagen-crosslinks, serum levels of parathormon, 1,25-dihydroxycholecalciferol and calcium, daily urinary calcium excretion) were investigated in 20 patients with RA. The treatment with 1 alpha-hydroxycholecalciferol resulted in an insignificant decrease in the number of swollen and tender joints, morning stiffness, CRP and ESR. Furthermore, a non-significant decrease in serum levels of TNF-alpha and IL-6 and an increase in IL-4 was observed. The treatment led to a significant decrease of bone-specific alkaline phosphatase (p = 0.001), osteocalcin (p = 0.04) and renal excretion of pyridinolin-crosslinks (p = 0.022) and to an increase of both serum calcium (p = 0.01) and daily urinary calcium excretion (p = 0.004). The results of this pilot study in a small group of RA patients indicate that an adjuvant therapy with active vitamin D metabolites may not only have preventive effects on systemic bone loss but also may inhibit the inflammatory and destructive process in RA in a limited degree.