Element profile patterns of growth and nongrowth phase hair were obtained for the C57L/J male mouse using a proton microprobe. Growth phase hair profiles of Cl, S, K and P show that these elements are concentrating in regions of higher pigmentation. Calcium is restricted to the medulla region in the hair shaft. For nongrowth phase hair, the profiles of Cl and S are essentially unchanged, whereas K and P are depleted in the hair shaft and are concentrating in the cornified root sheath. The element patterns found for the nongrowth phase profiles of mouse hair show striking similarities to previously reported patterns for growth phase profiles of human hair.