The effect of six different conjugated bile salts (two trihydroxyconjugated bile salts: tauro and glycocholic acids; and four dihydroxyconjugated bile salts: tauro- and glycochenodeoxycholic, tauro- and glycodeoxycholic acids) on eight bifidobacteria strains were studied. A strong growth-inhibitory effect was observed (80% at 0.95 mM) for each bile salt and strain. This phenomenon was explained by the production of deconjugated bile salt during bifidobacteria growth. The deconjugation phenomenon was concurrent with biomass production, and deconjugated bile salts were the sole compound produced during bifidobacteria biotransformation. In resting cell experiments, differences appeared between the strains and the kind of bile salts, particularly concerning taurocholic acid. The Bifidobacterium longum strains were the most efficient among the bacteria tested.