To assist in the assessment of the relative safety of chronically administered chlorine water disinfectants in man, a controlled study was undertaken. The study was conducted in three phases. Phase I, a rising dose tolerance investigation, examined the effects of single dose increasing concentration administration of chlorine disinfectants to normal healthy adult male volunteers. Phase II considered the impact on normal subjects of twelve week daily ingestion of the disinfectants at a concentration of 5 mg/L. In phase III, chlorite, at a concentration of 5 mg/L, was administered daily to glucose-6-phosphate dehydrogenase deficient subjects. Physiological impact was assessed by evaluation of a large battery of qualitative and quantitative tests. In general, the study affirmed the relative safety and tolerance of normal healthy adult males and normal healthy adult male G-6-PD deficient individuals to daily twelve week ingestion of 500 mL of chlorine disinfectants at a concentration of 5 mg/L.