The effects of exogenous abscisic acid (ABA) and polyethylene glycol (PEG 6000) treatments on grain H(2)O(2), ABA and beta-amylase activity were studied during grain development in the spike culture experiments with variety Triumph and its ABA-insensitive mutant TL43 as the plant materials. The results showed that during grain development the two genotypes were similar in the pattern of ABA concentration change, but differed greatly in the pattern of H(2)O(2) concentration and beta-amylase activity changes. The beta-amylase activity was positively correlated with H(2)O(2) concentration, negatively correlated with ABA concentration, and it is mainly closely associated with continued high levels of ABA with respect to H(2)O(2). Water stress (PEG treatment) induced beta-amylase was associated with H(2)O(2) concentration but not with ABA concentration. Exogenous application of H(2)O(2) and Ascorbic acid (AsA) increased beta-amylase activity in Triumph but reduced that of TL43. However, the endogenous H(2)O(2) concentration in grains was always consistent with beta-amylase activity. A novel model was hypothesized from the current results to illustrate the relationship between H(2)O(2), ABA and beta-amylase synthesis for the barley exposed to abiotic stresses.