Data on the bone metabolism of human immunodeficiency virus (HIV)-infected patients are still extremely rare. To investigate the influence of HIV infection on the calciotropic hormones and markers of bone metabolism, we therefore performed a cross-sectional study on 100 patients (65 males and 35 females) with proven HIV infection. The following criteria were used for exclusion from the study: age less than 20/more than 50 years, confinement to bed, wasting symptoms, treatment with agents containing ketoconazole, renal or hepatic insufficiency, clinical or echographic signs of liver cirrhosis, endocrine diseases, or treatment with medications known to influence bone metabolism. Bone mineral content (BMC) was determined by single-photon absorptiometry on the left forearm. Reduced BMC was found among the male and female HIV-infected patients. Additional long-term use of heroin resulted in a severe loss of mineralization in the respective females. The markers of bone metabolism were determined in urine and serum samples. Significantly lower osteocalcin concentrations were found, indicating a reduced bone formation rate whose severity showed a significant correlation with the progressive loss of CD4 helper cells and was independent of low vitamin D3 levels (1,25-dihydroxycholecalciferol) and alterations of protein metabolism. Increased urinary excretion of cross-links as an expression of enhanced bone resorption was likewise significantly correlated with the loss of CD4 helper cells and independent of the vitamin D concentration and protein metabolism. It is therefore concluded that the changes in bone metabolism are mainly due to mechanisms of the impaired immune defense of HIV-infected patients.