A method of aligning an agent distributor in an apparatus for generating a three-dimensional object comprises selectively depositing an agent on a layer of build material to form a predetermined alignment pattern (211, 212, 311, 312), and detecting the alignment pattern (211, 212, 311, 312) from a height profile in a surface of the build material, and performing an alignment operation using the detected alignment pattern (211, 212, 311, 312). An alignment pattern (211, 212, 311, 312) may comprise, for example, a series of triangles which are scanned to determine misalignment.