Disuse atrophy has been the subject of research studies of an animal model in which single-limb immobilization induces atrophic changes in the immobilized limb. These reveal systemic changes in the experimental animals that go far beyond the local response expected in that situation and are not fully understood as yet. We therefore performed a biochemical study on the effect of hind-limb immobilization on the serum and tissues of rats. The experiment was carried out on 70 young Sprague-Dawley male rats. In one group of 35 rats, the left hind-limb was immobilized for 3 weeks. Another group of 35 rats served as controls. Serum total protein, albumin, urea, creatinine, and calcium were found to be reduced during immobilization. Serum cholesterol levels, on the other hand, increased to a considerable extent. No changes were recorded with phosphate, bilirubin, and magnesium. Serum alanine aminotransferase (ALT) and alkaline phosphatase (ALP) were both reduced in activity. The activity of muscle aspartate aminotransferase (AST) and bone alkaline phosphatase (ALP) was also decreased. Lactate dehydrogenase (LDH) remained unchanged in both serum and muscle. We discuss our findings in the light of previous knowledge regarding the atrophic process.