The purpose of this study was to investigate the copy number of mtDNA in CD14+ monocytes and all cell populations circulating in the blood of patients with SSc and apparently healthy individuals and to assess the association of mtDNA copy number with pro-inflammatory status of monocytes assessed by IL-6 secretion by cultured monocytes under basal and pro-inflammatory conditions, mitochondrial activity, and clinical characteristics of patients with SSc. This evidence concerns the gene IL6 and systemic sclerosis.