Recently, as the secondary structure of protein structure has come to be distinctly reflected by the ultraviolet circular dichroism (CD) spectrum, an attention has been called to the protein structure of cell membrane by circular dichroism. Lenard and Singer have demonstrated by CD spectrum that the chemical fixation of the cell membrane induces changes in the structure of native red cell membrane, but it is not clear whether or not their conclusion is applicable in common to the membrane of other cells. One of the objects of the present study was to clarify whether the conclusion of Lenard-Singer can be applied generally. For this purpose the author studied changes in the protein structure occurring after the chemical fixation of mitochondrial particles of the rabbit liver and rabbit red cell membrane and bovine serum albumin. It seems quite significant to elucidate the general applicability of their conclusion by clarifying the conformational changes in cell membraneous proteins and other proteins induced by the chemical fixation as it would offer a great parameter to grasp the molecular structure of native cell membrane. The second objective was to elucidate the specific phenomenon, i.e. the cause of red shift of the cell membrane, by the circular dichroism. On the basis of the findings obtained in the observations of those changes occurring in mitochondrial particles, red cell membraines and bovine serum albumin after the chemical fixation, the author proposes here a dynamic cell membrane model as suggested by Seno. The results of the study may be briefly summarized as follows. 1) In the investigation of spectra of the BSA fixed with formaldehyde it has been clearly demonstrated that the aggregation of protein molecules induces the red-shift of the CD spectrum confirming the theory of Lenard-Singer to be valid. 2) Of the findings reported by Lenard-Singer, the facts that chemical fixation induces about 30% (corrected value, 50% ) adhesion of helical structure to the cell membrane, and that the chemical fixation with KMnO(4) brings about the loss of 100% helical structure of the membraneous protein molecules were also demonstrated similarly in the rabbit liver mitochondrial particles and rabbit red cell membrane, indicating that these findings are fairly common in all kinds of cells. 3) However, the extent of conformational changes in the cell membrane induced by the fixation with KMnO(4), OsO(4) or glutaraldehyde as concluded by Lenard-Singer differs from author's own finding. Regarding this problem it seems to be desirable to study further many other kinds of cells. 4) Noting the resemblance of the CD spectrum of BSA fixed with formaldehyde to that of the cell membrane, the author has assumed that the cell membraneous protein molecules are arranged in the form of aggregation. On the basis of this assumption the author has proposed a modified form of the unit membrane model. This modified unit membrane model has the possibility of being readily transposed to a particulate unit model and it has been designed from the perspective of the circular dichroids as against the dynamic membrane model proposed by Seno.