The stability of diluted solutions of sodium hypochlorite was studied. Sodium hypochlorite 1% solutions were diluted (1:8, 1:12, and 1:20) and stored at room temperature in a window exposed to sunlight in amber-glass, two-liter bottles that were two-thirds full. Samples were taken 25 times throughout a six-month study period; bottles were opened only on sampling days. An iodometric titration was used to determine the percent available chlorine in each sample. Least-squares regression analyses of the percent available chlorine yielded lines with negative slopes for each dilution (-7.7 X 10(-6), -8.1 X 10(-6), and -1.5 X 10(-6) for the 1:8, 1:12, and 1:20 dilutions, respectively). Using the fastest degradation rate (from the 1:12 dilution), 5.24% of available chlorine would be lost per year. The concentration of sodium hypochlorite would therefore remain above 90% of the initial concentration for 22.9 months. It is concluded that sodium hypochlorite solution stored in amber-glass bottles should carry a 23-month expiry date on chemical stability.