Abstract Chemiluminescence experiments were carried out with several transition metal complexes in fluid solution, using continuous and/or stop—flow techniques. The oxidation of Cr(II) polypyridine complexes by S2O82- led to luminescence emission from the 2Eg metal-centred excited state (2MC) of the corresponding Cr(III) complexes. The reduction of Ru(III) polypyridine complexes (including the mixed ligand Ru(bipy)2(DMCH)3+ complex) by OH− or C2O42- led to luminescence emission from the triplet charge transfer excited state of the corresponding Ru(II) complexes. The mixing of Cr(II) and Ru(III) polypyridine complexes led to luminescence emission from the 2MC of the corresponding Cr(III) complexes. The mechanistic and energetic aspects of these chemiluminescence processes are discussed.