Previously described results (7) led to the conclusion that although cycloheximide is translocated less easily in eastern white pine when compared with western white pine, the antibiotic tends to persist longer in the eastern white pine needle tissue, an effect which may have been due to the use of higher concentrations of the antibiotic. Present work supports this conclusion in so far as it confirms the persistence of low concentrations in eastern white pine needles for at least 57 days without detectable loss.The use of tritium-labeled cycloheximide to follow uptake and distribution of the antibiotic in pine seedlings demonstrates an accurate technique which appears to be widely applicable to studies of the translocation and persistence of cycloheximide.