Anaerobic degradation requires a diverse yet interrelated group of organisms. These organisms exist in a synergistic relationship that requires that a delicate balance be maintained for the system to function properly. Therefore, anaerobic treatment systems are frequenly consid,,red to be somewhat unreliable due to the sensitivity o- methanogens to toxic substances. Consiaerable researc has been done to determine reliable methods of predicting? when this balance has been upset. Formic Acid is a common intermmediate in anaerobic degradation and half of all methancgens can utilize it as a substrate. However, most of the research perferred regarding its role in anaerobic systems has focused acural rather then engineered. environments. Further, many of the methods used to analyze for formic acid require extensive pretreatment to remove interfering substances and the use of unstable enzymatic solutions and are not amenable to use as a process monitoring method. In this research an analytical method which could be routinely used for determining formic acid was developed. This procedure was utilized to examine the fluctuations of formic acid concentration in anaerobic batch reactors which were fed substrates containing various amounts of substances known to induce stress in these systems. The results were examined to determine possible correlation between these fluctuations and system performance;