Studies were conducted to investigate the crossability of the cultivated Brassica species, Brassica napus (oilseed rape), B. rapa (turnip rape), and B. juncea (brown and oriental mustard), with two related cruciferous weeds that are abundant in certain regions of Canada, Erucastrum gallicum (dog mustard) and Raphanus raphanistrum ssp. raphanistrum (wild radish).  Seed was produced without recourse to embryo rescue from all reciprocal crosses except R. raphanistrum x B. juncea.  Four hybrids were recovered, namely B. napus x E. gallicum, B. napus x R. raphanistrum (two plants), and B. rapa x E. gallicum.  The hybrids were characterized by their morphology, RAPD analysis, and cytological examination.  The B. rapa x E. gallicum hybrid was extremely vigourous and fertile, and would likely grow in natural habitats.  This hybrid produced self-seed and backcrossed readily with the B. rapa parent and, to a lesser extent, with the E. gallicum parent.  The B. napus x E. gallicum hybrid was a weak plant, but produced fertile backcross progeny with the E. gallicum parent.  The B. napus x R. raphanistrum hybrids were vigourous but mostly sterile.  Because of their low vigour and/or sterility, hybrids produced from crosses of B. napus with the cruciferous weeds would not likely be an environmental concern.  However, the potential of the B. napus x E. gallicum and  B. rapa x E. gallicum hybrids to backcross with E. gallicum may be of concern.