Aims: The present work aimed to define a minimal chemically-defined medium which could sustain the growth of most (if not all) strains of Streptococcus thermophilus. Methods and Results: A minimal medium containing 20 components, including one carbohydrate source, six amino acids, two metallic ions, six vitamins and urea allowed for growth of 13 out of 15 Strep. thermophilus strains. Growth of the two last strains required the presence of additional amino acids, the number of which depended on the strain. Growth rates of the strains in the minimal medium ranged from 0.38 to 0.64 h(-1), and final populations were about 10(8) cfu ml(-1). Conclusions: Streptococcus thermophilus appears much less demanding than other lactic acid bacteria. Significance and Impact of the Study: The definition of such a growth medium will be very useful for metabolic flux studies as well as peptide transport studies.