Natural abundance carbon-I 3 Fourier transform n.m.r.-spectra were obtained o f tke cyclic decapeptides /Phe4 Va16]antarnanide (11; antamanide (11); (Tyr']antamanide (HI); fAla' lantamanide (IV) and their ion complexes (1)-Na', (IJ-Na', (II)-Li+, (III)-Na+ and (IV)-Na+. Based upon literature data, systematic comparisons and model compounds, a line assignment approach was performed for the majority of the aliphatic carbons. The spectra o f the lAlay Val6] analogues ( V ) (Bystrov et al., 1972) and II (measured in CD3cN Patel, I 9 73a, b) and their complexes were also assigned. Characteristic chemical shift variations observed upon complex formation were calculated (A6 free peptideJMe+ complex) for a number of corresponding carbons, revealing shift changes up to 2.4p.p.m. Preliminary calculations of the 0 angle at selected prolines for some ion complexes are included.