This paper describes a study of fatigue crack initiation in WB36, a German low alloy steel, tested in high temperature, high purity, water. Flat un-notched, tensile specimens were cycled under load control, with R=0.1, and with a saw-tooth wave form (with a loading time of 30 seconds and an unloading time of 3 seconds). Crack initiation was followed by periodically stopping the test and replicating the surface. The tests were performed at 177°C, in water containing 8ppm O². H²SO⁴ additions were also made in some tests to raise the conductivity of the water from 0.06 μS/cm to 0.4–0.5μS/cm. The crack initiation and growth data are correlated with the water chemistry of the test.