Evaluation of fatigue crack growth behavior in Nb-H alloys was done using the Unified Approach to Fatigue Crack Growth developed earlier. It shows that the mechanism of hydrogen embrittlement changes with crack growth rate, load ratio and hydrogen concentration. The analysis provides an example where the changes in the governing mechanisms can be easily followed using the ΔK* vs Kmax* trajectory map discussed in the Unified Approach. Published by Elsevier Science Ltd.