The longitudinal relaxation rate ( 1 T 1 p ) of water protons was studied in solutions of Mn(II)-concanavalin A at a number of frequencies. These relaxation rates were lowered in the presence of a variety of saccharides which have affinities for concanavalin A which range over two orders of magnitude. A good correlation was found in which saccharides which bind tightly have the greatest effect and saccharides which bind weakly or not at all have little effect on the 1 T 1 p values. The temperature dependence of the proton relaxation rates showed that the lowering of these rates in the presence of saccharides was most likely due to a change in the exchange rate of solvent interacting with protein-bound Mn(II), 1 T m . An analysis of the temperature and frequency dependence of the 1 T 1 p and 1 T 2 p (transverse) solvent proton relaxation rates resulted in evaluation of a number of parameters for solvent water molecules interacting in the first coordination sphere of Mn(II) bound to concanavalin A. The ratio of the number of water molecules ( q) to the Mn(II)-proton distance ( r) obtained from a computer fit of the data over a limited temperature range is in accord with the findings of Koenig et al. ((1973) Proc. Nat. Acad. Sci. 70, 475) and Meirovitch and Kalb ((1973) Biochim. Biophys. Acta 303, 258). However, our studies of 1 T 1 p and 1 T 2 p of water over a more extensive temperature range are best fit with the following conclusions: at low temperatures (<20 °C), the data are consistent with an outer-sphere relaxation process. At higher temperatures (> 30 °C), the water molecule in the inner coordination sphere of the bound Mn(II) begins exchanging more rapidly and contributes to the relaxation processes ( 1 T 1 p and 1 T 2 p ). The relaxation time of protons in the inner coordination shell, T 1M, contributes over the entire temperature range and produces a frequency dependence in the relaxivity data from 6 to 100 MH z since the contributions to the correlation times are in the range 10 −9-10 −8 sec.