The defect model for LaMnO3+delta has been studied. The defects that are formed in LaMnO3+delta, are La and Mn vacancies in equal amounts. Thermogravimetric analyses indicate that the relation between composition (delta) and oxygen partial pressure can be described by charge disproportionation of Mn3+ into Mn2+ and Mn4+. The same model holds for (La,Sr)MnO3+delta. (C) 1994 Academic Press, Inc.