Large populations of viable buried arable weed seeds have been found in soil which has been continuously used as pasture for the last six years. Small numbers of dicotyledonous seedlings were found to germinate within the grass sward, but did not appear to become established. A disturbance of this soil, as caused by cultivation, resulted in a large flush of germination during the subsequent 4 weeks. Under laboratory conditions only 10 per cent of these seedlings emerged in the absence of illumination. Under field conditions there was no germination at all in the dark. A short ‘light-break’ of only 90 sec was sufficient to cause the germination of a large proportion of seeds. On the basis of these results it is concluded that the appearance of all weed seedlings from buried seeds, following cultivation, is dependent upon the exposure of these seeds to light.