The hypothesis was tested that slow grain drying stimulates pre-maturity alpha-amylase activity in wheat (Triticum aestivum L.). Grain drying rate in 91 commercial crops of cultivars Avalon or Mercia grown over the years 1988–90 was estimated from the slope of linear regressions of moisture content on time. Incipient sprouting was detected in some samples from 1988 using the fluoroscein dibutyrate test, but results from a beta-limit dextrin gel assay indicated that pre-maturity alpha-amylase was probably the major source of alpha-amylase activity in these samples. Although year-to-year differences in ln alpha-amylase activity and Hagberg falling number tended to be associated with seasonal differences in drying rate, there was no evidence of a relationship between either ln alpha-amylase activity or Hagberg falling number and drying rate after the year effect was removed by an analysis of covariance. A second dataset from one crop in each of 14 years at one site showed significant positive linear relationships between cumulative potential evapotranspiration calculated over different periods during grain ripening and Hagberg falling number (excluding 3 years when incipient sprouting was thought to occur). It was concluded that pre-maturity alpha-amylase activity was stimulated by an unknown environmental factor differing between seasons and associated with seasonal differences in drying rate and cumulative potential evapotranspiration.