Solid-state high-resolution C-13 and N-15 NMR spectra of microbial poly(epsilon-lysine) (epsilon-PL) derivatives with azo dyes have been measured. Chemically modified derivatives of epsilon-PL, epsilon-PL/MO and epsilon-PL/DC were prepared through reactions with methyl orange ( MO) and dabsyl chloride ( DC), respectively. Side chain alpha-amino groups of epsilon-PL in epsilon-PL/MO are involved in ionic bonds with methyl orange to form poly-ion complexes, (epsilon-PL)-NH3+SO3--(MO). On the other hand, epsilon-PL is allowed to react with dabsyl chloride in epsilon-PL/DC to form covalent sulfonamide bonds, (epsilon-PL)-NH-SO2-(DC). These chemically modified epsilon-PL's exhibit N-15 NMR signals characteristic of the binding mode at the alpha-amino groups. The spectral analysis reveals that the epsilon-PL/DC sample contains a small amount of ion complexes with MO. It has been shown that N-15 solid-state NMR is a useful tool for structural determination of epsilon-PL and its derivatives.