The 13 C and 1 H NMR spectra of the complexes of La III , Eu III and Lu III with 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane (L 1 ) in acetonitrile or methanol indicated the presence of two enantiomers the interconversion of which proceeds through both a ring inversion and a rearrangement of the pendant arms. The following kinetic parameters were extracted from temperature-dependent 13 C NMR spectra for the ring inversion in [LaL 1 ] 3+ , [EuL 1 ] 3+ , [LuL 1 ] 3+ in CD 3 OD and [EuL 1 ] 3+ in CD 3 CN: k(298 K) = 1396, 1055, 1288 and 880 s -1 ; ΔH ‡ = 37.6, 41.1, 48.2 and 47.7 kJ mol -1 ; ΔS ‡ = - 58.5, -49.2, -23.8 and -28.4 J K -1 mol -1 , respectively. The lanthanide(III) substitution induces a continuous variation of the kinetic parameters, implying the same pathway for the enantiomerization. The behaviour of [LnL 1 ] 3+ in solution is compared with that of complexes with similar 12-membered tetraaza macrocycles bearing pendant arms.