Nine bifidobacteria were tested for their tolerance to simulated gastrointestinal tract conditions at 37°C. Resistance to simulated gastric juice (pH 2·0 and 3·0) and bile salts (5 and 10 g l−1) varied among test strains. Bifidobacteria lactis Bb-12 was significantly more resistant to low pH and bile than any other test strain. Bifidobacteria adolescentis 15703, Bifidobacteria breve 15700, Bifidobacteria lactis Bb-12 and Bifidobacteria longum Bb-46, with the best overall resistance, were encapsulated in alginate microspheres (mean diameters of 20 and 70 μ m). Cold-stage scanning electron microscopy revealed groups of encapsulated bacteria in the porous alginate microspheres. The alginate microspheres retained their integrity at pH 2·0. Microencapsulation of bifidobacteria did not significantly improve survival over free cells when exposed to simulated gastric juice. Survival was improved for microencapsulated Bifidobacteria longum Bb-46 over that of free cells during refrigerated storage in milk with 2% fat. However, the presence of microencapsulated Bifidobacteria longum and Bifidobacteria lactis in milk resulted in off-flavours not found in samples with free cells, indicating the metabolism of entrapped cells had been altered.