Technical Abstract: In seeds and vegetative organs of barley and other cereals, thionins are processed into peptides with pronounced anti-microbial properties. In vitro studies demonstrated the toxicity of a- and ß-hordothionins (HTHs) to the fungal pathogen Fusarium graminearum. Increasing the expression of thionin genes may, therefore, provide resistance against this and other pathogens. Before a transgenic strategy can succeed, obstacles to Hth expression must be overcome. Barley transformed with a seed-specific barley aHth1 gene produced very little Hth1 mRNA in non-endosperm tissues. Removal of the first of two nearby 5’ methionine codons (producing aHth1') increased Hth1 mRNA levels. However, not even the association of Hth1 with membrane-bound polyribosomes led to HTH protein accumulation. Transformation of oat with this Hth1 vector (Carlson et al., 2006) showed that HTH1 protein was produced but only in the endosperm. These findings suggest that cereals have a mechanism (or deficiency) that prevents HTH1 protein accumulation beyond the endosperm. A ß-hordothionin cDNA, Lemthio1, cloned from lemma (hull) mRNA, produced high levels of LEMTHIO1 protein in lemmas of transformants. These will be tested for resistance to F. graminearum. In addition, we found that the population of the large thionin gene family variants was skewed toward cell wall bound forms. This may reflect the fibrous nature of the lemma.