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Intensive research over the past 10 years has produced many genetically-modified lines of oilseed rape with market potential . Assessment of these lines in statutory trials prior to their release as cultivars is necessary, owing to concern over the likelihood of transgene escape from such crops . Here, we examine the movement of airborne pollen grains from oilseed rape fields and assess their capacity for long-range geneflow .Pollen dispersal from isolated rape fields was monitored over two seasons and related to the distribution of fields and `feral' (domesticated plants growing outside cultivations) populations of the crop in Tayside and North East Fife regions of Scotland . Airborne pollen density declined with distance and at 360 m was 10% of that at the field margin . Pollen counts of 0-22 pollen grains m 3 were observed 1 .5 km from source fields and apparently were sufficient in number to allow seed set on emasculated bait plants . Oilseed rape pollen has greater capacity for long-range dispersal than had been suggested by small-scale field trials . Mean separation of oilseed rape fields in the survey area was 410 m and the mean distance from `feral' populations to commercial fields was 700 m . Sixty percent of `feral' populations with more than 10 plants occurred downwind and within 2 km of an oilseed rape field. Provided that the flowering biology of genetically-modified oilseed rape does not differ from the conventional crop, these data suggest that transgene movement to non genetically-modified fields or `feral' populations is likely following commercial release . 417