Cytosolic free Ca(2+)and intranuclear Ca(2+)behave similarly in human neutrophils. However, conventional laser scanning at 350 ms/frame resolution at lower than physiological temperatures demonstrates that (i) the nuclear fluo3-Ca(2+)signal persists longer than the cytosolic signal in some (but not all) nuclear lobes, (ii) the neutrophil nuclear membrane and fine inter-lobe filaments present barriers to diffusion of fluo3-Ca(2+)and lucifer yellow, and (iii) the diffusion barrier correlates with condensed chromosomal material on the nuclear envelope and blockage of the movement of fluo3-Ca(2+)into individual nuclear lobes.