ESDU 91015 gives crack propagation rate curves plotted against stress intensity factor range for various values of stress ratio of the alloys 2090, 2091, 8090 and CP 271 in unclad form and with various tempers. The majority of the data relate to behaviour in air, but some are for high humidity air, distilled or salt water, or dry argon environments. All the data are for long cracks under constant amplitude loading. The performance of the alloys is compared with that of more conventional alloys and the effects of stress ratio and environment are briefly discussed.