NH3 and CO2 concentration measurements performed on a Biological Water Processor (BWP), under development at NASA-JSC for water recycling, using near infrared laser diode absorption spectroscopy are reported. The gaseous effluents from the bioreactor are a concern for potentially introducing harmful amounts of NH3 in a spacecraft environment. Furthermore, NH3 and CO2 monitoring is important for understanding the nitrogen and total organic carbon (TOC) balance and conversion dynamics in the BWP, and real time continuous monitoring could reveal dynamic situations that are hard to detect otherwise. Diode lasers operating at wavelengths that access NH3 and CO2 absorption lines near 1.53 μm and 1.99 μm are used in a portable and automated gas sensor system. Concentration measurements were performed during a 16 day period starting in August 25, 2000, and a 5 day period starting in November 10, 2000. A sensitivity of 0.7 ppm (signal to noise ratio -SNR- ~ 3) with a precision of 0.2 ppm will be reported for ammonia, and of 1000 ppm (SNR ~3) for CO2. Ammonia levels up to 5.6 ppm were observed, with fluctuating dynamics that depended upon the operating conditions of the bioreactor. Carbon dioxide levels fluctuated from 0.05% to 3.5%.