The purpose of this study to examine whether vitamin D can reduce the activation of the immune system during dialysis. When activated, the immune cells release certain substances, called cytokines, which can be measured from small blood samples. We want to study to what degree the immune system is activated during a regular dialysis treatment and whether the time point of vitamin D administration, either right before the start or right at the end of a dialysis treatment, has an impact on the activation of the immune system.

Inclusion Criteria:

• Patient stable on chronic hemodialysis for more than 3 months.
• PTH level between 150 - 800 pg/ml.
• Ability to give informed consent.
• Serum calcium levels (corrected for albumin level of 4.0 g/dL) less than 10.5 mg/dL for the last three consecutive measurements.
• Serum Phosphorus levels between 2.5 and 7.0 mg/dL for the last three consecutive measurements.
• Ca x P-Product of less than 75 mg2/dL2 in the last three consecutive measurements.

Exclusion Criteria:

• Known active malignancy.
• Liver disease defined as serum aspartate aminotransferase, alanine aminotransferase, or gamma-glutamyltransferase levels more than 2 times the upper limits of normal.
• PTH levels between 150 pg/mL and 800 pg/mL.
• Hypercalcemia or hypercalcemic episodes within the last 4 weeks.
• Ca x P-Product more than 75 mg2/dL2 within the last 4 weeks.
• Any clinical significant infections which are or have been treated with antibiotics within 6 weeks prior to start of the study.
• Chronic viral infection (HIV, Hepatitis B or C).
• Currently on immunosuppressive medication (steroids, cyclosporine, etc…).
• Hematocrit less than 30 %.
• History of blood disorders other than renal anemia.
• Age of less than 18 years or more than 75 years.
• Hypersensitivity to paricalcitol or any ingredient of the product.
• Parathyroidectomy.
• Participation in another study at the same time.