During genetic sampling of white spruce in 1984, increment cores were taken from 80 populations in order to study wood density variation within species in natural Quebec forests. Results show that wood density differences exist between populations and that wood density is negatively correlated with the width of the growth rings; however, some trees and some populations exhibit both high wood density and rapid growth. A moderate positive link was found between juvenile and mature wood densities at both the individual and population levels. Therefore, breeding programs for the improvement of wood density could be based on selections made on juvenile wood.