FIELD and greenhouse studies with a number of herbicides have demonstrated various degrees of growth inhibition of young gymnosperm seedlings. The effects vary greatly with the chemicals and dosage used, species, age of plants, manner of herbicide application, and environmental conditions1–4. Considerable work has been carried out on herbicidal influences on metabolism of herbaceous plants, but very little information is available for the responses of woody plants. Triazine herbicides are generally accepted as inhibitors of photosynthesis5,6. Metabolism is probably altered by atrazine in red kidney bean7 and by simazine in barley roots8. The extensive literature on 2,4-D and 2,4,5-T shows that metabolism varies greatly with species, age of plant, and tissues tested9–12. Ingle and Rogers13 have shown that dalapon may reduce phosphate uptake while it does not alter respiration materially. EPTC causes some increase in respiration of mung beans and corn embryos after relatively long exposure to the herbicide14. Experiments have now been extended to evaluate the short-time effects of the active and inert ingredients of commercial formulations of several herbicides on respiration of tissues of woody plants. Herbicides and corresponding commercial formulations were obtained as: 2,4-D (esteron 10-10), 2,4,5-T (esteron 2,4,5-OS), 2,4-DEP (falone 44-E), EPTC (‘Eptam 6 E’), CDEC (‘Vegadex’), CDAA (‘Randox’), simazine (simazine 50 W), atrazine (atrazine 50 W), ipazine (ipazine 25 E), prometone (prometone 25 E), dalapon (‘Dowpon’), and sesone (sesone).