The research was conducted from March to July 2005 in order to determine the capacity of removing fecal coliform bacteria (FCB) and biochemical oxygen demand (BOD5) at "La Totora" Residual Waters Treatment Plant (RWTP) in the city of Ayacucho, Perú. Analyses were performed at the microbiology laboratory of the plant, where 70 water samples were analyzed. In order to quantify FCB, the Multiple Tube Fermentation (MTF) technique was employed and for BOD5, respirometry was used. With the results we calculated the percentage of FCB removal and BOD5 using the following formula: Removal% = [(C affluent-C effluent) / C tributary]x 100. The ability of BCF removal at "Totora" RWTP was 99.9850%, evacuating effluents with an average amount of 1.29 x 105 MPN/100 ml. This is poor, because to achieve an average amount of <103 MPN / 100 ml of BCF (Class III waters, General Law on Waters, DL 17752) RWTP should have a capacity of the removal of 99.9999%. BOD5 removal was 86.2%, with 46.35 mg / l evacuating effluents. This is also poor in relation to what is stated in the General Law on Waters. DL 17752 for Class III waters, which establishes a maximum concentration of 15 mg / l. In order to attain this concentration a removal of about 95.5947% would be required. [ABSTRACT FROM AUTHOR]