A research program is being conducted on the effects of air, helium, and sodium on the creep, creep-to-rupture, and fatigue properties of Type 316 stainless steel and 2 1/4 Cr1 Mo steel. The program is divided into eight tests according to contaminants (O, C, N) in the sodium; Tests 1 and 2 have been completed, and Tests 3 and 4 are in progress. A summary of the status of the program and the results to date is presented. (D.L.C.)