The great potential of exploiting growth-induced long-range atomic ordering for investigating strain relaxation in lattice-mismatched epitaxy is demonstrated by transmission electron microscopy (TEM) experiments performed on a CuPtB-type ordered (GaIn)P layer grown on top of a GaAs substrate. Due to the larger unit cell of the ordered structure compared to the zincblende structure of the disordered alloy some of the 60degrees misfit dislocations are no longer perfect dislocations, but are connected to antiphase boundaries (APBs) which were produced during the layer growth by dislocation glide. From the contours of these APBs in (110) cross-section TEM images, we are able to determine post-growth the layer thicknesses at which the individual 60degrees misfit dislocations were formed durin- the layer growth. This information is hardly available from any other technique. Apart from the problem of investigating a sufficiently large number of dislocations by TEM, this allows us to reconstruct the complete path of the strain relaxation. A striking feature revealed by the APBs is the simultaneous formation of many misfit dislocations with identical Burgers vectors at a layer thickness of about 12 times the critical thickness, indicating that dislocation multiplication took place during the layer growth. (C) 2002 Elsevier Science B.V. All rights reserved.