A hybrid molecule consisting of calmodulin (CaM) and the CaM-binding domain of olfactory nucleotide-gated ion-channel peptide (CaM-OLFp) was purified and crystallized by the hanging-drop vapour-diffusion method at 298 K. The crystals diffracted to a maximum resolution of 1.85 A at cryogenic temperature (100 K) using X-rays from a rotating anode (Cu, wavelength 1.54 A). The crystal belongs to the monoclinic space group C2, with unit-cell parameters a = 64.76, b = 36.23, c = 70.96 A, alpha = gamma = 90, beta = 109.4 degrees. Analysis of the packing density shows that the asymmetric unit contains one CaM-OLFp hybrid molecule with a solvent content of 36.42%.