In a double-blind trial, the effect on blood pressure of supplementation of normal milk (1180 mg Ca2+, 1650 mg K+ and 110 mg Mg2+ d-1) vs. 'mineral-poor' milk (95 mg Ca2+, 580 mg K+ and 10 mg Mg2+ d-1) was studied. Young healthy normotensive female students consumed one of the two supplements while on a low calcium diet (less than 500 mg Ca2+ d-1) for a period of 6 weeks. In both the normal milk- and 'mineral-poor' milk-supplemented groups systolic blood pressure decreased slightly. However, this decrease was persistently greater in the milk-supplemented group. The individual mean systolic blood pressure change during normal milk treatment (-4.1%) was significantly greater (P = 0.03) than that during 'mineral-poor' milk treatment (-1.3%). An effect of normal milk supplementation on diastolic blood pressure could not be demonstrated. The results of the present study indicate a small hypotensive effect of milk consumption, which is attributable to its content of essential minerals.