This work examines some of the factors that influence PHS in wheat, with particular emphasis on the premature production of alpha-amylase (PMAA) in the absence of visible sprouting. Field trials in 1989 and 1990 studied alpha-amylase activity in relation to grain development in four winter wheat cultivars. Weather conditions were generally warmer and drier than average in both years. Differences in drying rate were induced by covering and wetting treatments. Fenman had a slower rate of grain drying (40% - 23% moisture) than other varieties, but, within varieties, drying rate appeared not to be related to alpha-amylase levels. This lack of relationship was possibly due to the fact that all of the drying rates were relatively fast and, apart from Fenman, levels of alpha-amylase were low. The level of dormancy and the lack of visible sprouting indicated that the alpha-amylase activity observed in Fenman was due to PMAA. The increase in alpha-amylase began when moisture percentage was between 40 and 35% . Activity rose steeply, and remained high until harvest. There were differences in alpha-amylase activity between the wetting and covering treatments and the control in 1989, but these were not related to effects on grain drying. There was an increase in the number of grains with high alpha-amylase activity in the covered and wetted treatment and it was suggested that changes in microclimate at an earlier stage of grain development may have affected sensitivity to GA, leading to subsequent development of PMAA. This was investigated in 1990. The onset of sensitivity to GA₃ coincided with the increase in alpha-amylase activity in Fenman, but GA₃ sensitivity was also apparent in other cultivars that did not exhibit PMAA. Fenman showed an earlier onset of GA-sensitivity than the other varieties, but neither covering nor wetting had a significant effect on GA-sensitivity of PMAA.