Atomic force microscopy (AFM) has been used to observe modifications induced by a50-Hz 2-mT sinusoidal magnetic field on human B-lymphoblastoid cells (Raji). Cells exposed up to 64h showed adrastic decrease in cell height during the first 13h, reflecting the disappearance of microvilli, and aslower variation of the same parameter during the following 51h together with awidening and loss of the cells domed shape that corresponds to modifications at the cytoskeleton level.