The availability of the calcium contained in a high-calcium mineral water (Sangemini), popular in Italy, was compared in 18 healthy women with the availability of milk calcium ingested at the same calcium load, using 45Ca as the tracer in a randomized cross-over design. At an ingested calcium load of 2.5 mmol, absorption fraction averaged 0.433 for milk and 0.475 for Sangemini water. The mean quotient of the two (Sangemini/milk) was 1.129 (+/- 0.056, SEM, P < 0.05). The calcium of Sangemini water is thus highly bioavailable, and at least as bioavailable as milk calcium.