A placebo-controlled study was conducted to test the effect of Calpis (Calpis Food Industry Co, Ltd, Tokyo, Japan) sour milk, i.e., a milk fermented with a starter containing Lactobacillus helveticus and Saccharomyces cerevisiae, on the blood pressure of 30 elderly hypertensive patients, most of whom were taking antihypertensive medication. Subjects were randomly assigned to two groups. One group ingested daily 95 mL of the sour milk for 8 wk, and the other group ingested the same amount of artificially acidified milk as a placebo for 8 wk. In the sour-milk group, systolic blood pressure decreased significantly 4 and 8 wk after ingestion, by 9.4 +/- 3.6 mm Hg (mean+/- SE, P < 0.05) and 14.1 +/- 3.1 mm Hg (P < 0.01), respectively. The diastolic blood pressure also decreased significantly, by 6.9 +/- 2.2 mm Hg (P < 0.01), by 8 wk after ingestion of the sour milk began. No significant changes in blood pressure were observed in the placebo group. The decrease in systolic and diastolic blood pressure in the sour-milk group tended to be greater than in the placebo group. No marked changes were observed in other indexes, including pulse rate, body weight, and blood serum variables in both groups.