Abstract Crack growth in nickel-base alloys IN-738, IN-792 and René-80 at 927°C (1700°F) under cyclic and static loads was investigated using fracture-mechanics-type specimens. The influence of environment (specifically air, vacuum and impure helium) on crack growth was examined as well. Crack growth was markedly slower on a time basis in alloys under static load (creep) than under cyclic load (fatigue) and in creep required a higher stress intensity to be initiated. Generally the resistance to crack growth in creep was higher in air than in vacuum whereas in fatigue the converse was true. The creep crack growth rates in helium containing minute amounts of H 2, CO and CH 4 were not significantly different from rates in vacuum, the effect of impure helium being small at most. For a given stress intensity the fatigue crack growth rates among the alloys in air and in vacuum differed by only a small amount. Also the creep crack growth rates of the three alloys in vacuum did not vary greatly. The behavior of the alloys was generally similar to that of other nickel-base super-alloys observed previously.