Laboratory experiments were conducted to determine juglone sensitivity of 16 species (Trifolium incarnatum, Coronilla varia, Vicia villosa, Lespedeza stipulacea, L. cuneata, Acer ginnala, Caragana arbor-escens, Elaegnus angustifolia, E. umbellata, Lonicera maackii, Quercus alba, Fraxinus americana, Liriodendron tulipifera, Alnus glutinosa, Pinus strobus, andP. sylvestris) being considered for mixed plantings withJugions nigra (black walnut). All species were sensitive to juglone, but seed germination and radicle elongation were less affected than shoot elongation and dry weight accumulation. Seed germination and radicle elongation were affected by juglone in 6 and 11 species, respectively, mainly by the higher concentrations (10−3 M and 10−4 M). Shoot elongation and dry weight accumulation of all species were affected by juglone; many species were sensitive to concentrations as low as 10−6 M. Seedlings of all species were severely wilted and eventually killed by 10−3 M juglone, and most were chlorotic and severely retarded by 10−4 M juglone. Seedlings inhibited by 10−6 M and 10−5 M juglone did not showany visible signs of injury. Based on the effects on seedling shoot elongation and dry weight accumulation, the five species found to be most sensitive to juglone were:Lonicera maackii, Lespedeza cuneata, Trifolium incarnatum, Alnus glutinosa, and Elaeagnus umbellata.