Digital holographic microscopy (DHM) is a technique that allows obtaining, from a single recorded hologram, quantitative phase image of living cell with interferometric accuracy (Marquet et al., 2005). Specifically the optical phase shift induced by the specimen on the transmitted wave front can be regarded as a powerful endogenous contrast agent, depending on both the thickness and the refractive index of the sample. We have recently proposed (Rappaz et al., 2005) a new and efficient decoupling procedure allowing to directly obtain separate measurements of the thickness and the integral refractive index of a given living cell. Consequently, it has been possible, for the first time to our knowledge, to accurately measure (with a precision of 0.0003) the mean refractive index of living erythrocytes. On the other hand, the cellular thickness measurements allow to calculate the volume and shape of erythrocytes. In addition, DHM, thanks to its subwavelength phase shift measurements, was found to yield an efficient tool to assess erythrocyte cell membrane fluctuations (ECMF). Typically, ECMF characterized by an amplitude within the range of 45 nm were observed.