This study was undertaken to elucidate the intracellular changes of metal elements after the administration of fucoidan extracted from Cladosiphon okamuranus. TRL1215 cells (normal rat liver cell line) were treated with 0, 0.1, or 1.0 mg/ml fucoidan and incubated in 5% CO2 at 37 degrees C. The cellular levels of Mg, Al, Fe, and Zn were significantly increased in the 1.0 mg/ml fucoidan-treated cells compared to those of the 0.1 mg/ml fucoidan-treated cells and the control. Next, TRL1215 cells were cultured on Mylar film overnight. At 24 h after 5-bromo-2'-deoxyuridine dosing, 0, 0.1, or 1.0 mg/ml fucoidan was treated for 9 h. The cellular distribution of elements was analyzed using in-air micro-micro-particle induced X-ray emission. The X-ray spectra showed that yields of Al, Mg, and Zn were high in order of the 1.0 mg/ml fucoidan-treated sample, the 0.1 mg/ml fucoidan-treated sample, and the control. Fe yield was mildly increased by fucoidan administration. In fucoidan-treated cells, the focal accumulation of Br was correlated spatially with phosphorous-rich region, suggesting that Br was localized within the nucleus. Al distribution provided a spatial association with Br map. These data suggest that fucoidan increases the accumulations of Al, Mg, Fe, and Zn in normal rat hepatocytes, and fucoidan-binding Al is postulated to be transferred into the nucleus.