Linear polyesters of terephthalic acid of general formula --O--CO--C6H~--CO--O--(CHz),--(where n varied from 2 to 10) were irradiated with 6°Co v-rays. Irradiations were carried out at room temperature at a dose rate of 1"5 Mrad/hr to give a total dose of 1000 Mrad. DTA analysis showed that the number of--CH:--groups within the aliphatic part of the polymer chain influences both the enthalpy of melting of the original polymers and also the change in 3h r caused by irradiation. Polyterephthalates which contain an even number of--CHz--groups (even polymers) exhibit a hi~aer value of ±H, but radiation affects this value to a lesser extent than for odd polymers, especially in the range 4 ~< n ~< 9. In the presence of air, the decrease in ~H for irradiated polymers is more pronounced. Irradiation also leads to a decrease in the melting temperature, the change being greater for even polyterephthalates for 3 <~ n ~< 10 when irradiated in vacuum. In the presence of air, the change of melting temperature is more distinct for odd polymers for 4 ~< n ~< 9.