[en] Fatigue crack growth rate tests, at a load ratio of 0.2, have been conducted on steels of low, medium and high sulfur contents (0.004%, 0.013% and 0.025%) in PWR water at both low and high flow rates. Crack growth rates show no dependence on flow rate, but are strongly dependent on sulfur content, with a large proportion of environmental assistance for the highest sulfur contents. Tests of low and high sulfur content steels at a load ratio of 0.7 show relatively little environmental assistance in either case. The fractography of these specimens shows the usual brittle appearance for environmentally-assisted fatigue crack growth. In addition, the opposing fracture surfaces match perfectly, indicating that little or no dissolution of the metal matrix has occurred, and there is very little plastic flow associated with the fatigue cracking process. The x-ray photoelectron emission examination of the fracture surface oxides shows that FeS and FeS₂ coexist in the oxide layer, suggesting that the conditions within the crack enclave involved near-neutral pH and cathodic potentials