Gene flow from transgenic crops to related species has recently come into focus in risk-assessment studies of the ecological consequences of growing transgenic crops. This problem is especially serious in maize, as it is a representative wind-pollinated plant. We observed the hybrid percentage of maize seed and meteorological conditions for two years by using the xenia phenomenon. We examined the di#erences in the numbers of airborne pollen, meteorological conditions and the hybrid percentages

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... etween the two years, and discussed the e#ect of meteorological conditions on the hybrid percentage in the recipient maize field. The hybrid percentage at a distance from the donor field could be changed by several times depending on the meteorological conditions of the year. The spatial distribution of the hybrid percentage in the recipient field shows uneven and rugged structure. In ,**+, the dispersion of pollen ended in a comparatively short term, and the chance of hybridization was low. On the other hand, in ,**" the dispersion of pollen continued for a long term, and the donor pollen dispersed to a considerable distance in the recipient maize field. The chance of hybridization was high in general, and the observed hybrid percentages showed considerably high values under natural conditions.