A sample of cyclic oligo(undecanamide)s (1) (nylon 11 s), containing from the cyclic monomer to at least the cyclic hexamer, was conveniently prepared (57% yield) by the cyclo-oligomerization of 11-aminoundecanoic acid p-nitrophenyl ester under high dilution conditions. The cyclics, obtained free of linear oligomers by Virtue of their greater solubilities in chloroform, were analysed by fast atom bombardment mass spectrometry (FABMS), high pressure liquid chromatography (HPLC), gel permeation chromatography (g.p.c.) and H-1 nuclear magnetic resonance (n.m.r.) spectroscopy. The latter, which displayed a series of N-H signals reflecting the proportions of the various cyclics, was the most convenient method for analysing the cyclic oligo(undecanamide)s. A sample of cyclic alternating oligo(undecanamide-undecanoate)s (2), containing from the cyclic monomer to at least the cyclic undecamer, was conveniently prepared (57% yield) from (11-aminoundecanoyl)-11-oxyundecanoic acid p-nitrophenyl eater in a similar manner. Linear oligo(undecanamide-undecanoate)s (4) were prepared from the appropriate omega-bromo acid using a phase transfer catalysed reaction. These cyclic and linear oligomers, which were much more soluble than the corresponding oligo(undecananide)s, were analysed by FABMS, g.p.c., and H-1 n.m.r. spectroscopy. For these oligomers g.p.c. was the most convenient method of analysis.