The properties of water and hemoglobin in red cell suspensions were measured by NMR relaxation. Water exchange between cells and plasma was measured in the presence of low concentrations of Mn, and analyzed as a case of two-compartment exchange. The half-life of cell water was found to be 15 msec, at normal osmolarity. Both hemoglobin and water proton relaxation were measured in packed cells and concentrated solution, in H2O and D2O. Using selective excitation and detection, both the intrinsic relaxation of each proton system and the spin-transfer rate between them were separately determined. Large differences are observed between intact cells and solution, for the same hemoglobin concentration.