Fibroblasts obtained from patients with Friedreich's ataxia and normal control subjects were studied by immunocytochemistry for intermediate filament vimentin and also for in vitro proliferation. Trypsinized cells were seeded on coverslips and incubated for 1.5 h and 24 h. The expression of vimentin in cells was investigated by immunofluorescence microscopy. Cell proliferation was studied with BrdU antibody technique. Cells from patients with Friedreich's ataxia showed a slower outgrowth of vimentin filaments in comparison to cells from normal controls. These cells also incorporated less 5-bromo-2'-deoxyuridine (BrdU) into their DNA. The observations may be relevant to the clinical manifestations of the disease which involves many organs in addition to brain and spinal cord.