The rate at which chloroprene proliferates or polymerizes by the ’popcorn’ mechanism from the vapour has been measured by means of a McBain balance between the temperatures of 3 degrees C and 45 degrees C. First-order kinetics were found for growth over 2 or 3 days once an induction period was complete. The Arrhenius activation energy for the growth was found to be 38.4 +/- 0.7 kJ mol(-1).