Micromechanisms of fatigue crack growth have been studied in specific Ti3Al-based aluminides and TiAl-based aluminides. Effects of test temperature, environment and microstructure on fatigue crack growth resistance are considered. For both intermetallic systems brittle mechanisms of crack- extension are observed at room temperature, and such mechanisms persist in the TiAl-based aluminides considered to a test temperature of 800 o C. The implications of such observiations for the engineering application of these materials are addressed briefly.