Self-measured salt excretion from overnight urine samples shows significant correlation with 24-h-urinary salt excretion, but it is not known whether a self-measuring method can monitor daily fluctuations in individual salt consumption. In this study, we measured salt excretion from 24-h urine samples (24-h salt) in 50 volunteers over 3 test days (2 weekdays and 1 holiday), and examined to what extent the values correlated with estimates of 24-h salt excretion from overnight urine samples obtained using a self-monitoring device (ON salt). Urine collection was considered successful when the difference between the predicted and actual 24-h-urinary creatinine excretion was within 30%. Thirty-three (M/F = 7/26; 39.6 +/- 16.7 years) out of 50 participants completed their urine collections successfully and their samples were used in the analysis. Twenty-four-hour salt and ON salt did not significantly differ between test days and between the weekdays and the holiday. Moreover, there was a significant positive correlation between 24-h salt and ON salt for each test day. The coefficients of variation (CVs) for 24-h salt among test days and among subjects were 24.7% and 21.3%, respectively. The CVs for ON salt were lower than those for 24-h salt (13.3% and 17.7%, respectively). In conclusion, self-measurement of salt excretion from overnight urine samples allows estimation of daily salt intake; thus, the use of a self-monitoring device may be a useful motivational tool for personal salt restriction.