DNA content was measured cytophotometrically in Feulgen-stained nuclei of fusiform cambial initials from 1- (twig) and 19-year-old (stem base) cambia of balsam fir (Abies balsamea) trees throughout the season. Telophase (2C) and prophase (4C) DNA contents varied with both cambial age and time of year. Maximum DNA contents were observed at the beginning of cambial activity in April. They were lower in the 1-year-old cambium (42.3 (2C) and 84.3 (4C) pg DNA) than in the 19-year-old cambium (59.4 (2C) and 111.1 (4C) pg DNA). The DNA levels decreased during the cambial growing season, attaining minimal values in September of 28.3 (2C) and 53.5 (4C) pg and 37.9 (2C) and 74.5 (4C) pg in the 1- and 19-year-old cambia, respectively. In the autumn, cells accumulated in the G1 phase of the cell cycle. DNA synthesis then took place increasing the 2C levels from the minimum values to the maximum values. This DNA synthesis in 1-year-old cambia started before the beginning of the transition from the resting to the quiescent stage of dormancy.