Growth responses of a variety of human intestinal bacteria to methanol extracts of green tea (Thea sinensis L.) were investigated in vitro. The extracts moderately enhanced growth of some bifidobacteria strains in tests on carbon source-containing media but not carbon source-free media, suggesting that bifidus factor(s) might be involved. It did not stimulate growth of Clostridia, bacteroides, eubacteria or Escherichia coli. However, the extract was found to be selectively inhibitory against the growth of some Clostridia including C.difficile, C.paraputrificum and C.perfringens; this effect was not observed with bifidobacteria, eubacteria or E.coli.