Chemical stress may alter microbiological metabolism and this, in turn, may affect the natural and engineered systems where these organisms function. The impact of chemical stress was investigated using model chemicals 2,4 dinitrophenol (DNP), pentachlorophenol (PCP), and N-ethylmaleimide (NEM). Biological activity of Pseudomonas aeruginosa was measured in batch systems, with and without stressors at sub-lethal concentrations. Experimental results were interpreted with the Monod model to determine effects on growth parameters. DNP, between 49 and 140 mg/L, and PCP, at 15 and 38 mg/L, caused decreases in biomass growth yields, but did not inhibit substrate utilization rates. These effects increased with stressor concentrations, showing as much as a 10% yield reduction at highest DNP concentration. This suggests that a portion of carbon and energy resources are diverted from growth and used in stress management and protection. DNP, between 300 and 700 mg/L, and PCP at 85 mg/L caused decreases in growth yields and substrate utilization rates. This suggests an inhibition of both anabolism and catabolism. NEM was the most potent stressor, inhibiting biological activity at concentrations as low as 2.7 mg/L. The study also investigated whether adaptive responses are developed by pre-exposure to chemical stressors. It was found that pre-exposure weakened the microbial populations at specific stressor concentrations. These findings will ultimately be useful in better monitoring and management of biological treatment operations and contaminated natural systems.