The aim of this research was to isolate and characterise an efficiently expressed, leaf-specific gene from Beta vulgaris (sugar beet). Differential screening of a cDNA library derived from sugar beet leaf tissue was employed to identify mRNAs which are abundant and specific to sugar beet leaf tissue while absent in hypocotyl, or storage tissue. A leaf-specific gene, called sugar beet leaf -No. 1 (SBL-1), was further characterised by: (1) determining its abundance in the leaf poly (A)+ RNA population; (2) determining the DNA sequence of six independent SBL-1 cDNA clones; (3) carrying out Southern and Northern analyses to determine if SBL-1 belongs to a multigene family and what size transcript SBL-1 encodes, respectively, and (4-) using hybrid selected and hybrid arrested in vitro translation assays to determine the size of the polypeptide encoded by the SBL-1 open reading frame. From these analyses it was concluded that SBL-1, an 8.4-S transcript, comprises 1-3% of the poly (A)+ RNA population. At least three, and at most five, SBL-1 genes are present in the triploid sugar beet variety under study (Monoire) based upon cDNA sequences and Southern blot analyses, respectively. The SBL-1 cDNA was used to probe a genomic library constructed in the lambda replacement vector EMBL4.