Describes methods for the determination of stress corrosion susceptibility parameters of optical fibres. Dynamic fatigue and static fatigue tests are used to determine stress corrosion susceptiblity parameters, dynamic n-value and static n-value. Five test methods are described: Dynamic and static n-value by axial tension, dynamic and static n-value by two-point bending, and static n-value by uniform bending. These tests provide values of the stress corrosion parameter, n, used for reliablilty calculations in IEC 62048.