(1) Dietary deficiencies of Zn, Mg and K lead to a rapid drop in serum concentrations, with no change (Zn) or a slow decline (Mg and K) in the concentrations in skeletal muscle. (2) These deficiencies all lead to inhibition of growth and protein synthesis in muscle. (3) The inhibition of protein synthesis is faster in onset than the loss of Zn, Mg and K from muscle and therefore unlikely to result from cellular mineral deficiency. (4) The deficiencies are likely to be detected by the early drop in serum concentration, but the mechanism is unknown. (5) Possible mediators of growth inhibition are anorexia, GH and IGF-I. (6) Early detection of mineral deficiencies allows the organism to minimize wasteful protein synthesis and the formation of functionally inadequate tissues.