Two phase titanium aluminides with a lamellar microstructure of the intermetallic phases α2(Ti3Al) and γ (TiAl) are being developed for high temperature structural applications. Due to differences in lattice parameters and crystal structure, coherency stresses and mismatch structures occur at various types of semicoherent interfaces present in the material. The implications of these structural features on the stability of lamellar microstructures were studied by TEM in situ heating experiments. The investigations revealed that the lamellar interfaces serve as sources for perfect and twinning dislocations. The results will be discussed with respect to the observed degradation of the strength properties of the two phase alloys in the intended service temperature range of 900- 1000 K.