The relationship between sodium intake and blood pressure in adolescents was examined in a dietary intervention study. One hundred schoolchildren aged 11-14 years and representing the top, middle and bottom deciles of the blood pressure range completed a crossover protocol requiring them to raise and lower their sodium intake for alternate periods of 4 weeks. Blood pressure and urinary sodium excretion were assessed weekly and diet diaries were recorded at the end of each 4-week diet period. Diet-diary analysis confirmed that sodium intake was selectively affected by the intervention. Estimates of average urinary sodium excretion at the end of each diet period differed by more than 80 mmol/day. However, there was no significant change of either systolic or diastolic blood pressure, measured supine in the whole study group, in either sex or in any of the sub-groups, even in those children representing the highest blood pressure decile. Furthermore, the blood pressure changes seen in individuals during the crossover did not correlate with their changes in sodium excretion. This lack of effect of sodium on blood pressure is consistent with other dietary intervention studies in children and supports the hypothesis that the sodium sensitivity of blood pressure is age-related. We conclude that dietary sodium restriction alone has little potential for lowering blood pressure at an early age, even in children with higher than average blood pressure.