The objective of this study was to investigate the physiology and toxicology of Arcobacter in particular the type strain A. butzleri NCTC 12481. A. butzleri grew optimally at 25-35°C and pH 6-8. The presence of nitrate (0.1- 5mM) in the growth medium increased the growth rate. A. butzleri cells in the exponential phase were more resistant to heat than stationary phase cells (D₅₅ 1.1 & 0.4 min respectively) suggesting enhanced stress resistance. Heat treatment caused cell membrane damage shown by high fluorescence values due to the uptake of DNA-binding fluorescent dyes and more UV-absorbing material being released. At +4°C A. butzleri (stationary phase) viability decreased gradually, with increasing exposure time (1 x 10⁹ to 8 x 10⁵ cfu ml⁻¹, 21 day period). Freezing caused a 2 log decrease in viability after only 24 h in storage, thereafter the viability remained constant (0.6-1 x 10⁵ cfu ml⁻¹). No significant cytotoxicity (as determined by the MTT assay) was detected in either cell-free extracts from stationary phase cells or in the BHI spent media. Cytotoxic activity towards N2a and to a lesser extent ECV was detected in cell-free extracts from exponential phase cells. This toxicity was greater following heat treatment of the bacterial cells (55°C, 3 min) suggesting a membrane bound cytotoxin. Morphology studies showed that the toxin caused a decrease (>50%) in the number of neurite outgrowth on N2a cells. The toxin was heat stable and resistant to proteolytic enzymes. SDS-PAGE showed the presence of low molecular weight lipopolysaccharide in material released from cells in exponential phase. The most sensitive cell line was N2a, probably due to a greater abundance of CD14 lipopolysaccharide receptor on its surface. In conclusion, this study has quantified the growth and survival characteristics of A. butzleri NCTC 12481 and has demonstrated the production of an endotoxin by four human A. butzleri isolates.