4-Ethylphenol (4-EP) is a malodorant of swine waste and is derived from a component of lignin called p-coumaric acid (p-CA). The production of 4-EP from lignin in swine waste is untested. Additionally, the effect of Fe (III) on 4-EP levels is unknown. Four experiments were performed to determine if Lactobacillus sp. pep8 cultures, as well as enriched swine lagoon slurries, could liberate p-CA from lignin and convert p-CA to 4-EP. Furthermore, it was tested if the addition of Fe (III) influences the conversion of p- CA to 4-EP. Experiment 1 tested Lactobacillus sp. pep8 cultures to determine if the addition of 10 mM Fe (III) and 0.2% sulphite lignin to Lactobacillussp. pep8 cultures would stimulate production of 4-EP. Experiment 2 tested the effect of 0.2% sulphite lignin and 10 mM Fe (III) on 4-EP production in the presence of enriched swine lagoon slurries. On day 0 there was no detectable 4‐EP, for either 0.2% sulphite lignin addition or the 10 mmol l‐1 Fe (III) additions. Experiment 3 tested alternative forms of lignin, including 0.2% sulphite, indulin, or sigma lignin as potential source compounds for 4-EP production in enriched swine lagoon slurries. 4-EP produced in all three conditions are likely endogenous to the lagoon slurry additions. Experiment 4 was designed to measure the degradation of exogenous 4-EP with varying final concentrations of 4-EP in enriched swine lagoon slurries. Data in Figure 7 indicate immediate degradation of 4-EP by day 5, however, by day 7 synthesis of 4-EP occurred until day 14 where 4-EP levels remained in a steady state. Our results suggest that when both Lactobacillus sp. pep8 cultures and enriched swine lagoons are supplemented with p-CA, 4-EP is produced indicating that p-CA serves as a source of 4-EP. However, when supplemented with Fe (III) and/or sulphite, indulin, or sigma lignin, 4-EP production was not stimulated. This data indicates that, 4- EP production is not enhanced by the presence of Fe (III) in either Lactobacillus sp. pep8 cultures or in enriched swine lagoon slurries. Furthermore, lignin did not serve as a source of 4-EP.