In–situ neutron diffraction has been used to measure lattice strains parallel to two principal stress directions in biaxially-loaded AL6XN stainless steel. A new fixture was developed for loading thin-walled tubular specimens through combinations of internal pressure and axial loading. Under these conditions, the principal directions (σzz and σθθ in a cylindrical r, θ, z coordinate system) remain constant with respect to the initial crystallographic texture regardless of the level of biaxiality, a distinct advantage for diffraction experiments over the traditional tension/torsion tests for which this condition does not hold. Specimens were first pressurized to the level required to obtain a chosen value of σθθ. The axial load was then increased to reach the yield surface at different σθθ/σzz ratios, ranging from uniaxial to balanced biaxial loading (0, 0.4, 0.7, 1 according to Tresca). The {200}, {220}, {222}, and {311} reflections were measured in the axial and hoop directions as a function of axial load. A sequence of axial loading/unloading episodes was applied for different levels of plastic deformation. Under uniaxial tension, the {200} reflection showed the highest axial strains, followed by the {311}, and {220}/{222} reflections. With increasing internal pressure (biaxiality), the axial lattice strains corresponding to a given axial stress tended to decrease, and the responses of the various reflections tended to merge.