VDT workers are often exposed to static load in the shoulder stabilizing muscle due to repetitive work over long periods. Many investigations were reported the relationships between static load due to repetitive work and regional muscle disorder. However, diagnostic approach to work-related muscle disorder is difficult due to the absence of objective diagnostic tools. This study was performed to investigate the relationship between the serum CPK (creatine phosphokinase) concentrations and the shoulder muscle disorders. Results are as follow. 1. Mean serum CPK in total VDT workers was 67.6+/-28.4 IU/l and workers with abnormal serum CPK were 35 (21.5%). 2. Comparison between cases and controls did not show significant difference in the serum CPK level and the distribution of abnormal findings. 3. Sensitivity and specificity of the CPK test was 23.0% and 82.0%, respectively. Above results, in accordance with literatures, show that while serum CPK measure menu can be useful for the diagnosis of acute muscle injury, it does not adequately reflect the muscle disorders developed by the repetitive work of low tension over long time, such as VDT works.