Calbindin D(28K) is an EF-hand containing protein that plays a vital role in neurological function. We now show that calcium-loaded calbindin D(28K) interacts with Ran-binding protein M, a protein known to play a role in microtubule function. Using NMR methods, we show that a peptide, LASIKNR, derived from Ran-binding protein M, interacts with several regions of the calcium-loaded protein including the amino terminus and two other regions that exhibit conformational exchange on the NMR timescale. We suggest that the interaction between calbindin D(28K) and Ran-binding protein M may be important in calbindin D(28K) function.