Zinc deficiency negatively affects muscle function, but there are limited biochemical data identifying the cause of this reduction in function. The objective of the present study was to identify soluble proteins in rat soleus muscle that were responsive to different levels of dietary zinc. Rats (n=21) were fed diets containing three concentrations of zinc: 5, 30 and 200 ppm for 42 days. There was no difference in body weights of the rats consuming the 5-ppm zinc diet compared to the rats consuming the 30- or 200-ppm zinc diets; however, bone zinc levels were significantly decreased in the 5-ppm dietary zinc group. Individual soluble protein fractions were isolated from these muscles and the samples were prepared for two-dimensional polyacrylamide gel electrophoresis. The expression levels of four proteins were significantly depressed by dietary Zn depletion and supplementation, S-glutathiolated carbonic anhydrase, myosin light polypeptide 3, heat shock protein 20 and heart fatty acid binding protein. This is the first report that indicates that both Zn depletion and supplementation result in protein expression profiles that may negatively affect skeletal muscle function. These results indicate that there are specific signaling pathways that require proper Zn nutriture for maintaining optimal muscle function and suggest that the consumption of pharmacologic doses of Zn may be detrimental to muscle function.