An n.m.r. investigation of the chemical and morphological changes occurring during erosion in pH 7.4 phosphate buffer at 37 degrees C of melt-fabricated polyanhydride devices formed from copolymers of 1,3-bis(p-carboxyphenoxy)propane (CPP) and sebacic acid (SA) is reported. From sequence distributions determined using solution-state H-1 n.m.r. spectroscopy, the following order of anhydride bond lability was determined. SA-SA approximate to SA-CPP much greater than CPP-CPP, leading to preferential hydrolysis of aliphatic blocks within the copolymer chain. Solid-state H-1 and H-2 n.m.r, spectroscopy were used to investigate morphological changes occurring during erosion. Both indicated significant absorption of mobile water after cn. 10 h. Subtle variations in the symmetry of the narrow signals confirmed the changes in chemical composition apparent from high resolution H-1 n.m.r. analysis. In the initial stages, there was an increase in crystallinity attributed to preferential erosion of amorphous regions.