Complexes formed between L- and DL-serine (Ser) and L- and DL-threonine (Thr) and H+, Ni2+, and Cu2+ at intermediate pH values have been studied potentiometrically at 25 °C and I= 0.10 mol dm–3(K[NO3]). The complexes of H+ and Cu2+ have also been studied calorimetrically. Stereoselectivity in the Gibbs free-energy changes is insignificant. However, the standard enthalpy of formation of [Cu(L-SerO)2] is more favourable than that of [Cu(L-SerO)(D-SerO)](SerO = serininate) by a small but significant amount (1.7 kJ mol–1). This stereoselectivity is explained by outer-sphere co-ordination between Cu2+ and un-ionized hydroxy-oxygen donor atoms. The presence of protonated complexes of both SerO and ThrO with Cu2+ at pH ⩽4.8 has been demonstrated.