Candidate diffusion barrier coatings were applied to aluminum oxide and silicon carbide fibers, and consolidated in a gamma titanium aluminide alloy. Interfacial coatings of titanium carbide and titanium diboride were applied to the fibers using chemical vapor deposition, while calcium oxide coatings were applied from a solution. Sections of these specimens were vacuum encapsulated in quartz tubing and heat treated for 50 hours at 1100°C. The thermochemical stability of the fibers was evaluated using energy dispersive x-ray spectroscopy to compare the fiber-matrix interface of the specimens before and after heat treatment. Both the as-manufactured and the coated aluminum oxide fibers showed no discernable interaction with the titanium aluminide matrix. Titanium diboride effectively prevented the silicon carbide fiber from reaction with the matrix. The silicon carbide fiber which was coated with titanium carbide showed significant reaction between the fiber and the coating after heat treatment.