A scanning proton microprobe has been used to study the elemental distributions, including trace elements, in human skin fibroblast cells. Both normal fibroblasts and fibroblasts cultured from patients with Menkes' disease, an X-linked genetic disorder known to be associated with defective copper metabolism, were examined by the probe Cells grown in a copper-rich medium exhibited higher levels of intracellular copper but were found to be susceptible to the toxic effect of the elevated copper level. In normal maintenance medium the Menkes' cells recorded an average intracellular copper level six times higher than normal fibroblasts.