Complex formation between Cu2+ and several ligands, each containing two amino and two amide groups, has been studied potentiometrically and spectrophotometrically. A digital computer was used to determine the composition of the complex species formed and to calculate their stability constants. N,N′‐diglycyl‐1, 2‐diaminoethane and its homologues form 5‐, 6‐, 7‐, 8‐ and 9‐membered rings between the two amide groups, respectively. No tendency towards formation of binuclear species has been observed.