The main objective of this work was to investigate the expression of xylanase and cellulose genes from <I>Ruminococcus flavefaciens</I> when introduced into related Gram-positive bacteria including the rumen bacterium <I>Streptococcus bovis</I>. In addition the discovery, and isolation of the β(1,3-1,4)-glucanase gene of <I>S. bovis</I> in the course of this work may provide new possibilities to express foreign genes in <I>S. bovis</I> or in other Gram-positive bacteria. The main findings of this work are summarised below: 1. Genes encoding polysaccharidase activity from the strictly anaerobic rumen bacterium <I>R. flavefaciens</I> can be transferred by electroporation into the ruminal bacterium <I>S. bovis</I> and into other Gram-positive bacteria from different habitats, including <I>Lactococcus lactis, Enterococcus faecalis </I>and <I>Streptococcus sanguis</I>. 2. <I>XynD </I>and <I>endA</I> genes of <I>R. flavefaciens </I>can be expressed from their own promoters in these species. Among the bacteria used as hosts for gene expression, <I>S. bovis </I>gave the highest yields of active enzyme. The expression levels of both gene products were found to be higher in <I>S. bovis</I> than in <I>E. coli</I>. 3. The <I>R. flavefaciens </I>enzymes were mainly secreted in the culture medium of <I>S. bovis</I>; however in <I>E. coli</I> they were mainly cell-associated. 4. The full-length enzyme of <I>xynD</I> was detected in several Gram-positive bacteria, suggesting the effect of proteases may be less than in <I>E. coli</I>. 5. The general rearrangement of the introduced plasmid and genes were not found in Gram-positive bacteria and the genes seem to be stable in these organisms. However rearrangement of <I>xynD</I> was observed in some transformants of <I>S. bovis </I>JB1, although non-rearranged transformants were also obtained. 6. Expression of <I>endA</I> and <I>xynD</I> activity was affected by energy sources supplied to <I>S. bovis</I> cultures, reflecting the accumulation of lactic acid.