Technical Abstract: Pathogens, ammonia, odor, and greenhouse gas emissions are serious environmental concerns associated with swine production. This study was conducted in two manure pits (33,000 l each) to determine the influence of 1.5 or 3.0 g thymol/l and 80 mg/l urease inhibitor amendments on urea accumulation, coliform bacteria, odor, and methane emission. Each experiment lasted 18 or 19 days, during which time 30 to 36 250-ml samples (six per day) were withdrawn from underneath each pit and analyzed for urea, thymol, VFA, coliform bacteria, and Campylobacter. At the end of each experiment, six 50 g samples from each pit were placed in serum bottles, and gas volume and composition were determined periodically for 28 d. Compared to the control pit, VFA production was reduced 64 and 100% for the thymol amendments of 1.5 and 3.0 g/l, respectively. Viable coliform cells were reduced 1.68 and 2.88 log10 CFU/g of slurry for the 1.5 and 3.0 g thymol/l, respectively; and Escherichia coli were reduced 1.67 and 3.01 log10 CFU/g of slurry, respectively. Campylobacter was not detected in the pits treated with thymol, in contrast to 63% of the samples being positive for the untreated pit. Urea accumulated in the treated pits from day 3 to 6. Total gas production from the serum bottles was reduced 65 and 76% for thymol amendments of 1.5 and 3.0 g/l, respectively; and methane was reduced 78 and 93%, respectively. These results suggest that thymol markedly reduces pathogens, odor, and green house gas emissions from a swine production facility. The urease inhibitor produced a temporary response in conserving urea.