New values have been obtained for the magnetoelastic coefficients h, and k, of nickel at room temperature from ferromag- netic resonance experiments on (100) single crystal nickel films. The ratios of h,lh, and h,lh, are found to be 0.091 +_ 0.007 and 0.153 i 0.015, respectively, which giveh, = (-8.5 +_ 0.7) X lo4 and h, = (-14.3 + 1.4) X 1W6 if the Lee and Asgar value of h, is used (-94 X The magnetocrystalline anisotropy constant K,, the saturation magnetization M, and the spectroscopic splitting factor g also have been measured. It is found that K, = (-5.4 ? 0.3) X lo4 erg/ cm3 and that g = 2.161 +_ 0.009, in agreement with published data on bulk samples, but the value of A4 is found to be higher than the bulk value by 1.6%. The discrepancies between the values of h,, h,, and M as reported here and the bulk values are discussed. The theory of ferromagnetic resonance has been extended to cover the five-constant representation of magnetostriction and to the K, anisotropy term. The effect of the g factor having cubic anisotropy of the resonance conditions has been calculated,