The microtitration agglutination test (MAT) and the enzyme-linked immunosorbent assay (ELISA) developed to detect antibodies in pig sera against Treponema hyodysenteriae, were evaluated as methods to determine the prevalence of swine dysentery. Sera were collected from 3 age groups of pigs on 30 farms with either a history of swine dysentery (SD+) or determined as being free of the disease (SD-). Thirteen of 14 SD+ herds (93%) were detected with the ELISA when sera from market age pigs were evaluated. None of the 8 SD- herds were positive. The detection rates in the SD+ herds for the 2 tests by age group were: MAT--adults 1.4%, market 6%, weaned 0.8%; ELISA--adults 16%, market 31%, weaned 0.5%;Pigs recovered from swine dysentery caused by exposure to serotype 1 T. hyodysenteriae were resistant to subsequent exposure to the same isolate. Pigs recovered from serotype 2 T. hyodysenteriae, were resistant to subsequent exposure to serotypes 1, 2, and 4 T. hyodysenteriae;Treponema hyodysenteriae was found to survive in experimentally inoculated soil for 41 days at -20C, 18 days at 4C, 2 days at 22C, and less than 5 hours at 37C. Treponema hyodysenteriae was found to survive in dysenteric feces for 15 days at 22C and 74 days at 4C. In soil-to-pig transmission studies, T. hyodysenteriae was not transmitted to sentinel pigs placed in soil pen environments from which dysenteric pigs had been removed 4 hours, 5 days, and 6 days previously;The ELISA was concluded to be of sufficient sensitivity to be used to detect herds infected with T. hyodysenteriae, and thereby provides a way to determine the prevalence of swine dysentery. The market pig was the best age group to test with the ELISA for detecting the greatest number of animals demonstrating serum antibodies to T. hyodysenteriae, without giving false positive results;Cross-protection against clinical signs of swine dysentery was demonstrated to exist among 3 of the 4 serotypes of T. hyodysenteriae, including the 2 found in the United States;Treponema hyodysenteriae can survive in soil and feces for various periods of time, however, soil environments did not appear to be important for the transmission of swine dysentery.