Cadmium alters the temporal dynamics of various cellular proteins, including heat shock proteins and protooncogenes. To reveal the molecular dynamics during cadmium cytotoxicity, we investigated the conventional nucleocytoplasmic transport pathways. Western blot analyses revealed that exposure of porcine kidney LLC-PK₁ cells to cadmium (10 μM) temporally induced HSP 70 and Ran in the cytoplasm and Ran and RCC1 in the nucleus. RCC1 could be detected in the nucleus as early as 1 hr after exposure of the cells to the metal. Thus, HSP70-Ran-RCC1 transport system appears to be involved in early phase cadmium cytotoxicity.