The fragmentation of derivatives of 9,10-dihydroanthracene and of its heterocyclic analogues containing atoms of O, S, N, P, Si, As, Se and Te at positions 9 and/or 10 is examined. The conditions reviewed are electron impact and chemical ionisation with recording of positive and negative ions. It has been shown that depending on its nature, the heteroatom may be eliminated together with substituents from the molecular ion or a substituent may be lost both as a radical and together with an additional H atom. The fragmentation of compounds in which the substituting groups are adjacent to the heteroatom is explained by the "peri-effect". The elimination of substituents from phenylene rings, at the meso position and at the heteroatom occurs in a similar manner to elimination in the corresponding aromatic derivatives. © 1991 The British Library.