Rumen cannulated Holstein steers, fed corn silage and a corn-soybean grain mixture twice a day, were used to compare the effectiveness of heat and formaldehyde treatments in preserving the amino acid profile of soybean meal exposed to ruminal fermentation for 12h. Formaldehyde treatments were 0, .3, .6, and .9g/100g soybean meal. Defatted soybean flakes treated at 250, 250, 215, and 180°C for 30, 20, 20, and 25min, respectively, and unheated soybean meal comprised the heat treatments. The in situ polyester bag technique was used to obtain estimates of ruminal degradation of the treated and untreated soybean meals and to obtain undegraded residues from the soybean meals following 12h of rumen exposure. Diaminopimelic acid was used to assess the extent of bacterial contamination. Significant amounts of apparent diaminopimelic acid were detected in unexposed samples (2.0 to 7.6% of soybean nitrogen) and in residues (4.8 to 12.7% of residue nitrogen). Significant differences in amino acid contents were detected between untreated and heat-treated soybean meals and their respective residues. Formaldehyde treatment was effective in preserving the original amino acid profile of soybean meal.