Expression of foreign genes in Escherichia coli requires the juxtaposition of prokaryotic transcription and translation elements with a coding region for the foreign gene. Commonly, this results in only modest expression of the foreign gene product. Here we describe a novel ribosome-binding site (RBS; phage T7 'gene 10 leader') which is able to drive the translation of several foreign genes. This RBS dramatically enhanced the translation efficiency of all the genes we have tested to date, and was particularly effective for foreign genes. The enhanced expression was often more than 40-fold greater than that obtained using a 'consensus' RBS. A general plasmid vector has been constructed, incorporating the T7 gene 10 leader sequence, which allows the facile expression of important gene products. In this report we demonstrate the application of this system for the high-level expression of plant, mammalian and bacterial proteins in E. coli.