We have studied the compatibility of Ag and (Co,Cu)Z-hexaferrite with the composition Ba3Co1.4Cu0.6Fe24O41 (Z). In order to do this, the (Co,Cu)Z-hexaferrite was cofired with various amounts of Ag at 900 degrees C. The degradation of the (Co,Cu)Z-hexaferrite to Y- and U-hexaferrite occurred during the cofiring and was confirmed by X-ray diffraction as well as by thermomagnetic measurements. The permeability and permittivity of the cofired ceramics were measured in the range 1 MHz to 10 GHz. For the (Co,Cu)Z-hexaferrite, both these properties were significantly influenced by the Ag when the amount of Ag exceeded a minimum of 4.5 wt%. The influence of the Ag and the degradation of the (Co,Cu)Z-hexaferrite on the permeability were evaluated using the Bruggeman effective media theory.