Pressure tubes in CANDU(6) and RBMK reactors are fabricated from Zr-2.5Nb alloy. This paper describes the mechanical properties of tubes used in power reactors made by four routes using electrolytic powder as the base material. The microstructures developed by each route are distinct: CW: cold-worked material consists of flattened alpha-Zr grains surrounded by a skin of beta-Zr phase; used in CANDU 6 reactors. CW-A: material that was cold-worked and annealed at 540 degrees C contains elongated alpha-Zr grains mixed with equiaxed alpha-Zr grains and particles of beta-Nb phase; used in all RBMK 1000 reactors, TMT-1: material quenched from the (alpha+beta)-Zr phase into waterfollow by cold-working consists of alpha'-phase and between 10 and 20% of untransformed alpha-phase; used in RBMK 1500, Ignalina 1. TMT-2: material quenched from the (alpha+beta)-phase into argon-helium gas mixture followed by cold-working consists of Widmanstatten alpha-phase and untransformed alpha-phase. This material is used in RBMK 1500, Ignalina 2. The CW and TMT-2 tubes have a higher proportion of grains with basal plane normals in the transverse direction, F-T of 0.52 to 0.57, than in the radial direction, FR of 0.38, while quenched and annealed materials (TMT-1 and CW-A) have similar values of FT and FR, about 0.38 in quenched materials and 0.41 in annealed materials. Transverse tensile strength, crack growth resistance, dJ/da, and axial crack velocity, V-H, of delayed hydride cracking (DHC) were evaluated, using standard techniques, between 250 and 300 degrees C on as-fabricated materials. In-reactor creep deformation was evaluated from measurements of tube diameter in RBMK 1000s, RBMK 1500s and two CANDU 6 power reactors. Strength and crack growth resistance were measured on TMT-1 and TMT-2 tubes removed from Ignalina NPP Units 1 and 2 after 12-17 years of in-reactor service. As-received cold-worked material had the highest strength; the annealed material had the lowest strength while the quenched materials had intermediate strength. Irradiation increased the strength by about 200 MPa in all four materials. Although DHC is sensitive to texture and the distribution of the beta-Zr phase, the dominating factor controlling crack velocity appears to be material strength: with an increase of strength by a factor of about two, V-H increased by a factor of 30. Since harmful trace elements were well controlled during manufacturing, other factors affecting crack growth resistance could be assessed. Again, strength appeared important; dJ/da declined approximately linearly with increase in strength induced by irradiation, decreasing from about 350 to 100 MPa as the strength increased from about 250 to 850 MPa. The exception was TMT-2 material where crack growth resistance was maintained after irradiation. TMT-2 material also had good diametral creep resistance in-reactor, attributed to both its texture and grain structure. The other three materials had similar creep resistance controlled mostly by their texture.