Our objective was to create a standardized and reproducible inflammation model in chickens in order to study the pharmacodynamics of several anti-pyretic and anti-inflammatory drugs. We studied the influence of age and repeated lipopolysaccharide (LPS) administration on body temperature and the correlation of this with concentrations of interleukin-6 and IgM antibodies against LPS in plasma of chickens. Three-week-old and 5-week-old broilers were injected intravenously with LPS from Escherichia coli O127: B8 at a dose of 1 mg/kg. LPS administration was repeated after 2 or 7 days. After the first dose of LPS, the body temperature was initially decreased below normal and then later increased above normal. The second dose of LPS reduced the level of hypothermia and the duration of the febrile phase. Three-week-old birds responded to LPS with a higher maximum body temperature and a greater area under the body temperature versus time curve than 5-week-old chickens (P<0.05). Interleukin-6 reached its highest concentration 3 h after LPS administration and returned to baseline levels after 9 h. A second dose of LPS resulted in a significantly lower peak in interleukin-6. Significant higher levels of antibodies against LPS could be detected 7 days after LPS administration. However, there appeared to be no correlation between the reduced response to LPS and the presence of antibodies.