The dissociation behavior of several species of proteoglycan aggregates (PGA) has been studied quantitatively by monitoring the changes in particle size by dynamic laser light-scattering. Firstly, studies of the thermal dissociation of reconstituted PGA from bovine nasal septum and bovine fetal epiphysus are described. The effect of link protein in stabilizing reconstituted PGA against changes in temperature has been demonstrated. It was also confirmed that, upon prolonged heating at 70 degrees, the dissociation of link-containing, reconstituted PGA is effectively irreversible. Secondly, the dissociation characteristics of native PGA isolated from chick chondrocyte and rat chondrosarcoma cell-cultures were investigated in aqueous solvents containing increasing concentrations of guanidine hydrochloride. It was found that the more densely packed, native, aggregate structure has a higher susceptibility to thermal disruption than the reconstituted, link-containing material. Considerable loss of subunits from the native aggregates occurs at temperature where the link protein retains its activity. The dissociation of native PGA is irreversible, in the sense that reconstituted PGA always exhibits smaller sizes than the native PGA, reflecting a smaller degree of aggregation of the subunits.