Stem‐unit measurements could be useful for early selection if these dimensions were highly heritable and strongly correlated with traits of commercial interest, such as height growth. Height increments and the number and length of stem segments were mesured in the first and second growth period in predetermined and free growth of Douglas‐fir seedlings from 40 families in each of 2 populations from southwestern Oregon. Populations, or families in populations, exhibited genetic variation in all traits except number of stem units in predetermined growth. Heritabilities for stem‐unit measurements were higher than those for height increment in the first growing season, but not in the second. Correlations among measurements of stem units and height increments were only moderate (generally <0.70). Stem units are not likely to be better measurements of height in early selection of Douglas‐fir than are measurements of either predetermined or free growth.