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The differential display method was used to identify a novel barley gene, Lem1, expressed primarily in the outer organs (lemma and palea) that enclose developing florets and seeds. The promoter was isolated from a BAC genomic clone and used in a translational fusion with a green fluorescent protein gene (Gfp) to produce a transient expression vector. After particle bombardment, Gfp was expressed only in lemmas, paleas and awns of developing spikelets. Lem1 did not promote Gfp expression in vegetative leaves or in mature spikes, although expression of co-bombarded uidA (GUS) occurred under the regulation of a ubiquitin promoter. This reproduced the developmentally regulated pattern of mRNA accumulation. Deletion studies showed that the promoter activity is confined to a cis element within 80 bp of the transcription start site. Upstream from this, the promoter contains putative auxin-, ethylene- and gibberellin-responsive elements or homologues. Lem1 was found to be a single intronless gene encoding an acidic 102 amino acid protein, possibly associated with membranes. In a two-rowed barley, Lem1 mRNA was absent in the lateral spikelets, which fail to develop, and present only in the developing median spikelets. This suggests that Lem1 may play a role in organ development.