Haemoglobin molecules isolated from normal human subjects have been directly micrographed under the electron microscope following in general Hall's technique. The average height (h) and the widths along (w11) and perpendicular (w⊥) to the shadow direction of the molecules have been measured as 56.5 ± 6.6 A, 122.7 ± 15 A, and 120.9 ± 20 A, respectively. The exaggeration in the molecular widths due to the deposition of metal cap ranges between 60 to 70 A. The probable resolution of the substructure of the molecule, e.g., presence of "holes" and dimples, in the present electron microscopic evidence has been discussed. The electron microscopic results on the size of the individual haemoglobin molecules are in satisfactory agreement with the recent x-ray diffraction model of Perutz and his associates for horse haemoglobin.