As genetically engineered crop varieties near widespread cultivation, both agronomic and environmental concerns mandate the development of effective strategies for isolating transgenic varieties from related non-transgenic varieties or cross-fertile weeds. We present the results of the first field experiment designed to test the effectiveness of two containment strategies that are commonly used in field trials of transgenic crops: (1) an isolation zone devoid of vegetation to discourage emigration of insect pollinators from transgenic plots; and (2) trap crops (non-transgenic varieties of the same crop planted adjacent to the transgenic plot that can 'cleanse' emigrating pollinators of transgenic pollen). In conjunction with field trials of genetically engineered canola (Brassica napus) conducted by Calgene, Inc., in California and Georgia, we varied both the width of the barren zone and the presence or absence of a trap crop, and measured the effects on gene escape. Escape was easily detected since the genetic construct inserted into the transgenic canola contained a gene that rendered seedlings resistant to the normally lethal antibiotic kanamycin. Our results suggest that barren zones 4-8 m in width may actually increase seed contamination over what would be expected if the intervening ground were instead planted entirely with a trap crop. When trap crops occupied a limited portion of the isolation zone separating transgenic and non-transgenic varieties, the effectiveness of the trap depended on the width of the isolation zone: they reduced gene escape when the two varieties were separated by 8 m, but increased escape across a 4-m isolation zone. We conclude that, for the relatively short isolation distances we examined, the most effective strategy for reducing the escape of transgenic pollen is to devote the entire region between transgenic and non-transgenic varieties to a trap crop.