The induction and subsequent intracellular distribution of the 72-kDa heat shock (stress) protein (Hsp72) by exposure of cultured human alveolar (L-132) cells to dimethylarsinic acid (DMAA), a main metabolite of inorganic arsenics in mammals, were examined. A significant induction of Hsp72 in the cells was observed by exposure to 10mM DMAA for 6 h. The induction was similar to the case by arsenite for 6 h or by heat treatment at 42 degrees C for 3h. However, the nuclear distribution of Hsp72 differed greatly between DMAA and 42 degrees C treatment or arsenite exposure, i.e., Hsp72 induced by exposure to DMAA accumulated not only in the nucleoli but also in the nucleoplasm, whereas that by 42 degrees C or arsenite exposure did not accumulate in the nucleoplasm. Furthermore, the Hsp72 accumulated in the nucleus by DMAA exposure hardly diffused with the addition of ATP, suggesting that the DMAA-induced Hsp72 strongly binds to some macromolecules in the nucleus. The fact that Hsp72 induced by DMAA exposure accumulated in the nucleus of the cells may reflect a protective response toward the nucleus-specific damaging action of dimethylarsenics.