We have recently demonstrated the use of renewable reagent fiber optic sensors in a harsh sample matrix and with multiple reagent chemistries. Sodium hydroxide concentrations ranging from 1. 5-23. 0 (w/w) (0. 38-7. 2 M) were measured with a single probe chemistry. A sensor for free and total chlorine has been developed in which the reagents were sequentially switched to make the sensor responsive to either free chlorine (N 1 4-phenylene-diamine (DPD) + phosphate buffer) or both free and combined chlorine (DPD + phosphate buffer + KI). The detection limit of free chlorine was 0. 05 mgfL Cl2 at a reagent flow rate of4 j. tLtmin and covering a dynamic range of 0. 05-25 mg/L Cl2. Improvements in sensor fabrication techniques are currently being investigated in order to increase overall sensor functionality.