Single crystals of face-centered cubic cobalt have been examined between 4.2° and 850°K. The usual transformation to the hexagonal structure below 700°K is avoided by using two special forms of samples: (a) thin films evaporated onto MgO substrates, and (b) the precipitated cobalt-rich phase in a 2% Co–Cu single crystal. In both cases the fcc cobalt is stabilized by and has a close correspondence with the host lattice. Standard ferromagnetic (electron-spin) resonance techniques have been used to determine the magnetocrystalline anisotropy parameters K1/M and K2/M over the temperature range indicated, and, in addition, the spectroscopic splitting factor g is found to be 2.06±0.03 independent of temperature. The temperature dependence of the anisotropy constants is in accord with the relation K(T)/K(o) = [M(T)/M(o)]n, where for M(T)/M(o) we have taken the determination by V. Jaccarino [Bull. Am. Phys. Soc. 4, 461 (1959)] of the temperature dependence of the cobalt-nuclear magnetic resonance frequency which we assume to be proportional to the magnetization. The results that are obtained indicate that the power n of the dependence noted is nearly 10 for K1 and much higher for K2. At 0°K samples of type (a) have — K1/M = 600 oe.