Gene introgression from crops to weedy relatives has become an important issue with the development and release of transgenic crops. This study investigates hybridization between rape and a New Zealand population of wild turnip (Makarewa, Southland). The rape used was a rapid cycling non-transgenic line, homozygous for a single dominant mutation conferring resistance to the herbicide chlorsulfuron. Seed from wild turnip plants were harvested following hand pollination in a greenhouse and after natural pollination in field trials that were conducted at two ratios of rape:wild turnip, 1:1 and 1:~400. Interspecific hybrids were identified in the progeny populations by in vitro screening of seedlings for resistance to chlorsulfuron. Their hybrid status was confirmed by DNA content using flow cytometry. As expected, hand pollinations produced 100% hybrid progeny, illustrating a high potential for interspecific hybridization between rape and wild turnip. In contrast, hybrids were very rare under natural field conditions.