We have calculated the exchange and correlation corrections to the free energy (F xc) and the chemical potential (μ xc) of an electron system at arbitrary degeneracies and temperatures. These are needed for density-functional, average-atom-type calculations of properties of plasmas and liquid metals. The problem of inverting the parametric relation between μ xc and the density correction n xc is considered. We present easy-to-use analytic fits to F xc and μ xc as functions of the temperature and density. We also consider the effect of a lineraly responding ion background on the electron chemical potential as well as the ion chemical potential, as these are needed in calculations of ionelectron systems at arbitrary degeneracies and densities.