Cuttings were collected from the field between September and May, when buds and cambia are dormant, and were placed under favorable conditions in environmental cabinets. Radial width of new xylem, measured at the midpoint of the cuttings, was used to indicate cambial activity.In bud-bearing cuttings, cambial activity was associated with bud activity. Debudding decreased cambial growth. Application of a mixture of indole-3-acetic acid (IAA) and lanolin to the apex of debudded cuttings promoted cambial activity in a manner similar to that effected by expanding buds. Clearly, bud-produced auxin is required for cambial activity in balsam fir.Cambial activity increased with increasing preexposure to natural chilling until about December; thereafter additional preexposure did not further increase cambial growth. Extending the natural chilling period with a period of artificial chilling enhanced cambial growth in material collected during the autumn, but not in material collected later. The effect of chilling was manifested whether or not buds were present during the chilling period. Long photoperiod partly compensated for lack of chilling in autumn-collected material. It is concluded that the cambium of balsam fir in central New Brunswick has an autumnal rest period that grades into quiescence by about December. Cambial rest was not broken by applications of IAA, gibberellic acid, or kinetin, or by IAA with either of the others.