AbstractWith the objective of comprehending abnormal metabolisms of the essential metals of zinc (Zn) and copper (Cu) in three groups of skin diseases, skin cancer, inflammatory diseases, and non‐inflammatory disease, we measured serum levels of Zn and Cu in 151 cases of various cutaneous manifestations and estimated the significance of the ratios between the two metals (Cu/Zn). The serum level of Zn was significantly decreased in cases of bullous pemphigoid, decubitus ulcer, and alopecia areata. The serum level of Cu was elevated in cases of psoriasis, decubitus ulcer, and skin cancer. We observed no elevation of serum Zn level or abnormally depressed serum Cu level. The Cu/Zn ratio showed significantly different values among these three groups of the diseases, suggesting the utility of measuring Cu/Zn ratios for differential diagnosis over that of determining the serum level of Zn or Cu alone. It was also demonstrated that, in each skin disease, the Cu/Zn ratio clearly reflects the severity of the progres