6-Aminosaccharin and related monomers were subjected to polymerization as melts and in solvents. The products from these studies passed through soluble, hemipolymer stages corresponding to polyamide structures before being cyclized at higher temperatures to the final, insoluble, thermally stable polymers. Melt polymerization of 6-aminosaccharin as the triethylamine salt was the preferred procedure and yielded products of highest intrinsic viscosity (0.431 dl/g in N,N-dimethylacetamide).