Although the value and use of mercurial diuretics for the treatment of advanced congestive heart failure has been thoroughly established, there remains the necessity for controlled evaluation of the various preparations useful for this purpose. Studies on mercupurin and salyrgan,1mercurial suppositories2and orally administered salyrgan-theophylline3have been reported from this laboratory. It is our purpose in this paper to present data on the effectiveness and safety of Mercupurin4administered orally in the routine treatment of congestive heart failure. STUDIES ON HOSPITALIZED PATIENTS A total of 42 patients was studied, of whom'32 were hospitalized and 12 were ambulatory; 2 patients were included in both groups. For the hospitalized patients two schemes of administration of the Mercupurin tablets were utilized. Whenever a diuretic was considered to be necessary, either a single dose of 5 tablets (with the exception of 1 patient who received 6 tablets) was given