Pronounced differences in the tolerance of tomatoes and bell peppers to clomazone observed in field studies were confirmed in a greenhouse experiment. In greenhouse studies, preemergence clomazone rates causing 50% visible injury on bell pepper and tomato seedlings 10 days after application were 9.4 and 0.1 kg/ha, respectively. Based on growth inhibition, bell peppers were 40-fold more tolerant of clomazone than tomatoes 20 days after clomazone application. In laboratory studies investigating the basis for differential clomazone tolerance, no differences in uptake of 14C-clomazone from nutrient solutions between tomato and bell pepper plants were observed after 24 h. Minor differences were observed in the distribution of 14C label within plants; a higher percentage of 14C was recovered in bell pepper roots than in tomato roots, while the opposite was true for the shoots. Clomazone was metabolized to two products in roots of both bell peppers and tomatoes within 48 h after treatment. Tomato shoots were more active in converting clomazone to these metabolites than were tomato roots. Bell pepper roots converted more clomazone to metabolites than did tomato roots 24 h after treatment. However, by 72 h, differences in clomazone metabolite levels between species were negligible in both roots and shoots. Enzymatic and acid hydrolysis of soluble, polaf clomazone metabolites indicated that these metabolites may be sugar conjugates of clomazone.