Many microorganisms fail to degrade pollutants when introduced in different natural environments. This is a problem in selecting inocula for bioremediation of polluted sites. Thus, a study was conducted to determine the success of four inoculants to degrade p-nitrophenol (PNP) in lake and industrial wastewater and the effects of organic compounds on the degradation of high and low concentrations of PNP in these environments. Corynebacterium strain Z4 when inoculated into the lake and wastewater samples containing 20 micrograms/ml of PNP degraded 90% of PNP in one day. Addition of 100 micrograms/ml of glucose as a second substrate did not enhance the degradation of PNP and the bacterium utilized the two substrates simultaneously. Glucose used at the same concentration (100 micrograms/ml), inhibited degradation of 20 micrograms of PNP in wastewater by Pseudomonas strain MS. However, glucose increased the extent of degradation of PNP by Pseudomonas strain GR. Phenol also enhanced the degradation of PNP in wastewater by Pseudomonas strain GR, but had no effect on the degradation of PNP by Corynebacterium strain Z4. Addition of 100 micrograms/ml of glucose as a second substrate into the lake water samples containing low concentration of PNP (26 ng/ml) enhanced the degradation of PNP and the growth of Corynebacterium strain Z4. In the presence of glucose, it grew from 2 x 10(4) to 4 x 10(4) cells/ml in 3 days and degraded 70% of PNP as compared to samples without glucose in which the bacterium declined in cell number from 2 x 10(4) to 8 x 10(3) cells/ml and degraded only 30% PNP. The results suggest that in inoculation to enhance biodegradation, depending on the inoculant, second organic substrate many play an important role in controlling the rate and extent of biodegradation of organic compounds.