The constant-compliance and applied-moment double-cantilever beam tests for adhesive fracture energy have been adapted to the measurement of the adhesion of thick-film metallizations on alumina substrates. The thick-film tests involve beams soldered to metallization strips and measure the strain energy release rate, G_c The fracture results are compared with peel strengths from solder-wire peel tests of the same metallizations. Both the fracture and peel tests indicate failure in the thick films but near the film/alumina boundary. The constant-compliance and the peel test data exhibit a bimodal distribution. The magnitude of the fracture energies indicate that failure usually occurs in the glass phase of the film but that film adherence is greatly enhanced by interlocking between the metal and glass phases. This interlocking and thus the film adhesion are strongly dependent on firing time and temperature.