Three trials were conducted to evaluate the effect of moniliformin (M) on performance and immune function in chicks. Day-old chicks were randomly assigned to four dietary treatments (0, 50, 75, or 100 mg M/kg diet). In Trial 1, chicks were placed on treatments for 3 wk and were injected intravenously with 4.6 x 10(6) Escherichia coli on Day 21. Blood samples were collected at 60, 120, and 180 min after inoculation, and liver, spleen, and lung were collected at 180 min postinjection. Compared with control chicks, chicks fed 75 and 100 mg M/ kg diet had higher (P 0.05). For the in vitro study, lymphocyte proliferation decreased linearly (P < 0.01) with increased concentrations of M. In all three trials, chicks fed 100 mg M/kg diet had lower (P < 0.05) feed intake and weight gain than did control chicks. Data from the current study suggested that M decreased performance and immune response in chicks at the level of 75 mg/kg diet.