The glass transition temperatures (T-g) of a 6/6.9 random copolyamide series have been investigated as a function of copolymer composition. The analysis was carried out using the technique of differential scanning calorimetry, and the degree of crystallinity was determined by wide angle X-ray diffraction. It was found that conventional models for determining T-g values do not fit the copolymers of this study. An appropriate description is achieved by considering a model that accounts for molecular interactions. Both hydrogen bond content and degree of crystallinity lead to the observed deviation in T-g from the values predicted by conventional models.