One of the challenges with using ethanol co-products is the potential for increased dietary S concentration. Dietary S concentration has been implicated as a cause of polioencephalomalacia (PEM) in ruminants. The focus of this research was to evaluate PEM in ruminants fed distillers dried grains plus solubles (DOGS) based finishing rations. Two separate hypotheses were formed: 1) Providing increased dietary thiamin will decrease the incidence of PEM in lambs fed increased S diets without affecting animal performance; and 2) Feeding DDGS would increase concentrations of H2S gas and incidence of PEM compared to diets based on dry-rolled com. Two studies were conducted utilizing lambs to evaluate either 1) the influence of increasing supply of dietary thiamin (0, 50, 100, or 150 mg/d) on performance and incidence of PEM when fed diets containing 60% DDGS or 2) the influence of DDGS inclustion (0, 20, 40, or 60% DM basis) on sulfur balance. A third study was conducted using beef steers to examine the influence method of com processing (high-moisture vs. dry-rolled com) and concentration DDGS (20, 40, or 60% DM basis) on animal performance, H2S concentrations and incidence of PEM. Hydrogen sulfide gas concentrations were measured via rumenocentesis as lambs and steers were adapted from a receiving diet to a finishing diet. No differences in lamb performance were noted (P 2: 0.17) when diets containing increasing concentrations of thiamin were fed. Sulfur excretion increased (P :'S 0.01) with increasing dietary DDGS. Lambs fed elevated concentrations ofDDGS had a 3 fold increase in water intake and a 4.8 fold increase S excretion via urine compared to lambs fed no DDGS. Steer performance decreased (P :S 0.02) with increasing concentration of DDGS. Hydrogen sulfide gas concentrations did not differ (P 2: 0.06) until d 14 when lambs fed 60% DDGS had greater H2S concentrations (0.23 ± 0.039 g/m3; P :S 0.006) than all other treatments. Lambs fed 60% DDGS continued to have greater (P :S 0.001) H2S gas concentrations throughout the adaptation phase compared to the other treatments. Lambs fed 150 mg ofthiamin per day and steers fed 60% DDGS had the greatest concentrations of H2S (1.07 g H2S/m3; P :S 0.009; 1.38 g H2S/m3, P :S 0.01), respectively). Ruminal H2S concentrations in steers were affected by increasing DDGS concentration in the diet (P < 0.001), but not by com processing method (P = 0.94). Ruminal pH was not affected by a day x treatment interaction (P = 0.65) or by treatment (P = 0.32), but decreased (P < 0.001) across the adaptation phase from 5.82 (d-7) to 5.33 (d 35) in lambs fed increasing concentrations of DDGS. The use ofthiamin as a dietary additive to aid in the prevention of PEM in finishing lambs does not appear to be necessary under the conditions of this study. Com processing did not influence animal performance or H2S concentrations in our study. Steer performance decreased when DDGS level was> 40% (DM basis); however lambs fed 60% DDGS had similar performance compared to lambs fed lesser amounts ofDDGS. The role dietary S from DDGS plays in incidence of PEM is questionable as no cases of PEM were observed with dietary S concentrations exceeding 2-3 times the maximum tolerable level. Additional research may be needed to clarify species specific observations and responses to dietary S levels.