Studies of Fe, Co, Al and Ga substitution for Cu in YBa2Cu3O7-δ have reported contradictionary conclusions about wether micro-twinning or a true orthorhombic-to-tetragonal transition occurs at ≈ 2.5% substitution. 89Y NMR has been used to study the structural change with doping of Co, Al or Ga for Cu in YBa2Cu3O7-δ. NMR is a microscopic probe and the chemical shifts is sensitive to the local atomic arrangements within the first few neighbours shells. For these substitution, the changes in 89Y chemical shift provide evidence which suggests that there is an orthorhombic-to-tetragonal transition. © 1993.