Cocumber (Cucumis sativus, L.) and wheat (Avena sativa L.) were used a test plants for determination of DIURON in two soils: sandy soil (Arenito Bocucatu) and clay loam (série "Luiz de Queiroz". The rates of herbicide applied for 400 g of the soils were: 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 10.0, 15.0 and 20.0 mg. Cucumber is very sensible to DIURON and may be used for determination up to 1.0 mg/400 g of soil; and wheat from 1.0 to 20.0 mg.