Samples of commercial nylon 7 were given different thermal or precipitation histories. Structure and crystallinity were followed by d.s.c., solid-state n.m.r. and attenuated total reflectance Fourier transform infra-red spectroscopy (ATR FTi.r.). Heat of fusion and melting temperature values ranged from 52 to 93 J g(-1) and 228 to 242 degrees C, respectively. Surprisingly, annealing did not give material with the greatest heat of fusion although it possessed the highest melting point. Solid-state C-13 and N-15 n.m.r. methods were used to observe the amorphous and crystalline fractions. For example, the amide nitrogens show resonances near 86.5ppm in amorphous domains, near 84ppm in alpha-crystals and near 89 ppm in gamma-crystals. N-15 cross-polarization/magic angle spinning spectra of solution cast samples contained peaks consistent with all three domains in various intensity ratios but with the gamma-peak being the most intense for most samples. Solid-state C-13 spectra contained peaks which supported the presence of these phases but with the or-phase peaks predominating. Treatment of solution-cast thin films with aqueous KI/I-2 gave materials whose n.m.r. spectra contained peaks consistent with these three phases in different ratios than for the initial solution-cast samples. Spectra of the melt crystallized samples contained peaks for amorphous and a-domains only. C-13 spin-lattice relaxation (T-1) magnetization decays could be fit to two or three exponentials (T(1)s of hundreds of milliseconds, a few seconds and hundreds of seconds) consistent with semicrystalline polymer behaviour. T-1 values for the long-relaxing component ranged from 350 to 23s for the annealed and precipitated samples, respectively. Amide V bands near 682 cm(-1), assigned previously to the cc-phase, were present in the ATR FTi.r. spectra of all the samples. However, the chemically treated and solution cast samples contained additional bands at 690 and 620 cm(-1) due to the gamma-phase. Spectra of quenched samples contained bands not seen in the other spectra.