The results of 3000 urine analyses are presented. The observational data were obtained for the reference group of school children and adults and for groups of people suffered from indoor mercury pollution. A novel Zeeman atomic absorption spectrometer and cold vapor and pyrolysis methods were used for determination of total mercury. A background mercury value in urine for St. Petersburg region is determined as 0.5 мg/l. Distributions of mercury concentrations in urine after five accidents are given. There are considerable differences in total mercury distribution for each group that depend on level of Hg exposure. Peculiar features of the 24-hour rhythm of mercury excretion with urine is used for the treatment of patients, an optimal therapy selection and rehabilitation control.