Ti-48.5Al-1.5Mo (at.%) and Ti-48.5Al-1.5Mo-X (X = 0.3, 1.0 and 2.0C or N) alloys were prepared by vacuum are melting and homogenized at 1390 degrees C for the lamellar microstructure and then aged at 900 degrees C. It was found that C (or N) additions decreased the grain size of the lamellar structure. In particular, 1.0 and 2.0%C (or N) additions refined the grain size to 1/10 of that of the mother alloy. Tensile elongation at room temperature decreased for the alloys with 0.3%C (or N) but recovered with 1.0%, and 2.0%C (or N) additions compared to the value of the mother alloy. The yield stress at room temperature for these alloys containing 1.0% and 2.0%C (or N) increased up to twice that of the mother alloy, and this high stress was maintained up to 800 degrees C. The aged alloys showed much higher tensile elongation at room temperature than did the alloys with only heat-treatment. Moreover, the alloy with 1.0%N added exhibited better creep resistance than did the mother alloy, in spite of its much smaller grain size. (C) 1997 Elsevier Science S.A.