Bekkedahl has shown that crude rubber at atmospheric pressure freezes in the temperature range from −40° to + 10°C. and melts in the temperature range from 6° to 16° C. The transition is from amorphous rubber to crystalline rubber which is the stable modification between −72° and 6° C. His measurements of the freezing at 0° C. showed that about 280 hours were necessary for completion of the transition, the volume decreasing by 2.2 per cent in such a manner that the volume-time curve was S-shaped. This communication reports the inhibition of crystallization at high pressure. Crude smoked sheets were packed tightly in a pressure chamber and isopropyl alcohol was used to transmit the pressure. The chamber was kept at 0° C. in a well-circulated ice bath. A pressure of 8000 kg. per sq. cm. was applied, and its constancy observed over a period of 14 days. The sensitivity of the manganin gauge used for pressure measurement was such that changes of 5 kg. per sq. cm. were detectable. Outside of slight erratic pressure changes caused by change of temperature around part of the press that was not kept at 0°, “no change of pressure due to crystallization was detected during the 14 days.” Examination of the rubber immediately after pressure was released showed that it was still in the amorphous state.