Biofiltration is a promising technology for reducing odor and gas emission from livestock operations. Tqo important operating parameters in biofiltration – media mixture content (MC) and gas retention time (RT) were studied to determine there effcets on sulfur and nitrogen balances. Laboratoru experiments were carried out to determine S and N accumulations in and emissions from biofilters with various media (MC 30%, 40%, 50%) and RT (5, 10, 20sec). The biofilter media was a mixture of compost and wood chips. The media bed was .20m deep and 0.30m in diameter. Two trials were run. Results showed that 47% to 94% of the hydrogen sulfide and 25 to 90% of ammonia were removed by the biofilters. Removal efficiency varied with treatment. Biofilters with 50% MC and 20 sec RT had the highest removal efficiency for H2S and ammonia, with the average H2S removal rates of 92.8% in trial 1 and 94.2% in Trial 2. Average ammonia removal efficiencies of these biofilters were 90.3% in trial one and 75.8% in trial 2. N and S accumulation in the biofilter media was also affected by MC and RT.