AbstractGlyphosate and glufosinate‐ammonium herbicide tolerance traits were combined into both winter and spring lines of Brassica napus L. This allowed the study of possible interactions between these transgenes in two genetic backgrounds when treated with a variety of herbicides. Selective herbicides that are commonly used within Brassica crops showed no adverse effects on the transgenic plants or their null controls. Lines containing both glyphosate and glufosinate transgenes remained tolerant to their respective herbicides, regardless of the presence of the second tolerance transgene. Lines containing only a single transgene retained tolerance to the encoded trait and did not show cross‐tolerance to the second. Null lines were killed by either herbicide. All plant lines, regardless of their transgene content, were found to be equally susceptible to three herbicides (paraquat, metsulfuron‐methyl and mecoprop), commonly used to remove volunteer B napus from succeeding crops and set‐a‐side land.© 2002 Society of Chemical Industry