The relevance of calcium (Ca2+), an essential bone mineral, to the prevention and treatment of osteoporosis is well established. However, a good deal of evidence casts doubt on the validity of current RDAs (recommended daily allowance), i.e., 800-1000 mg/day. New guidelines consistently advocate higher daily intakes (up to 1500 mg/day), a goal that may be difficult to achieve for many patients. Environmental as well as individual behavioral factors may limit the consumption of dairy products, whereas calcium supplements require a high level of compliance and cause additional costs. Calcium-rich mineral waters may offer a promising alternative. A systematic literature search was performed (Medline, years 1966-1998) to identify experimental studies on the bioavailability of calcium-rich mineral waters. First, all publications on calcium absorption from mineral waters were identified, and, in a second step, studies comparing calcium absorption from mineral waters with that from dairy products. Four studies fulfilled all inclusion criteria. A meta-analysis based on published p values indicated calcium absorption from mineral waters was significantly higher (p = 0.03) than that from dairy products. Although only few studies with a relatively small number of subjects are available to date, the bioavailability of calcium from calcium-rich mineral waters thus seems to be at least comparable to, and possibly better than, that from dairy products. These results are in keeping with the assumption that calcium-rich mineral water is a useful calcium source to achieve new, higher recommended daily allowances of calcium.