Technical Abstract: Defatted seedmeals from fifteen glucosinolate-containing plant species were analyzed for bioherbicidal activity by determining inhibition of seedling emergence when added to a sandy loam soil containing wheat (Triticum aestivum L.) and sicklepod [Senna obtusifolia (L.) H. S. Irwin & Barneby] seeds at rates of 0.1, 0.5 and 1.0% (w/w). Added seedmeals were generally more phytotoxic to wheat than sicklepod seed germination. For wheat, all of the seedmeals significantly inhibited seedling emergence at the 1.0% level. At the 0.1% rate three of the seedmeals {brown mustard [Brassica juncea (L.) Czern.], money plant (Lunaria annua L.), and field pennycress (Thlaspi arvense L.)} completely inhibited wheat germination. For sicklepod germination, eight of the seedmeals were completely inhibitory at the 1% rate {brown mustard, field pennycress, arugula [Eruca vesicaria (L.) Cav. subsp. sativa (Mill.) Thell.], Siberian wallflower (Erysimum x allionii), English wallflower [Erysimum cheiri (L.) Crantz], garden cress (Lepidium sativum L.), sweet alyssum [Lobularia maritima (L.) Desv.] and evening-scented stock [Matthiola longipetala (Vent.) DC.]} and four were completely inhibitory at the 0.5% rate (brown mustard, arugula, English wallflower and sweet alyssum). Intact glucosinolates and their corresponding hydrolysis products varied among the seedmeals with the highest activity. Major hydrolysis products produced by the seedmeals with the most phytotoxicity, respectively, included 2-propenyl (allyl) isothiocyanate (AITC) by brown mustard seedmeal, allyl thiocyanate and AITC by field pennycress seedmeal, erucin (4-methylthiobutyl isothiocyanate) by arugula seedmeal, 3-butenyl isothiocyanate and lesquerellin (6-methylthiohexyl isothiocyanate) by sweet alyssum seedmeal, and isopropyl isothiocyanate by money plant seedmeal.