A new selective medium for the detection of bifidobacteria was developed. The medium owes its selectivity to the presence of propionate (15 g/l) and lithium chloride (3 g/l) as inhibitory agents, and raffinose (7.5 g/l) as a selective carbon source. In addition, casein (5 g/l) is used as a protein source, which results in a zone of precipitation around the colonies of bifidobacteria. The medium, Raffinose-Bifidobacterium (RB) agar, is free of antibiotics and easy to prepare. Bifidobacteria growing on RB agar show a yellow colony with a yellow halo and a precipitation zone around the colony. All human and dairy bifidobacteria grew well on RB agar, except for some Bifidobacterium bifidum strains. Some uncommon or animal species, Bifidobacterium gallicum, Bifidobacterium asteroides, Bifidobacterium animalis, Bifidobacterium pullorum, and some Bifidobacterium bifidum either did not grow or did not show the characteristic reactions. No non-bifidobacterial strains used in dairy products grow with the distinctive characteristics. Some faecal strains showed good growth and acid production, resulting in characteristic reactions. These strains were Actinomyces species, a Clostridium perfringens strain and some lactobacilli of animal origin. Comparison with other media indicated that RB agar is more selective than other media used.