in the reported experiments, the effects of site, tree age, and position within a tree on the unbleached brightness and brightness response of black cottonwood refiner mechanical pulps from four areas of b. c. have been investigated. unbleached pulp brightness was consistently highest for 20-year-old trees and lowest for 80-year-old trees; it was also highest for the middle sections of all trees and lowest for the lower sections. the bleaching response to hydrogen peroxide varied unpredictably with site and tree age, but pulps from 20-year-old trees consistently gave the highest brightness and those from 80-year-old trees, the lowest. although the utilization of short-rotation black cottonwood from all four sites is preferred, the upper, maximum acceptable rotation age and/or potential value of any particular pulpwood procurement area should be determined by evaluatiing a much larger, representative sample of trees with ages bracketing the values indicated by the preliminary study described. 1 ref