Recent data suggest that Fusarium trichothecenes may reduce broiler performance at levels previously thought not to affect this variable in chickens. In the present study, we investigated the effects of deoxynivalenol (DON), a type-B trichothecene, on broilers. Male broilers at 7 d of age were fed either a basal diet (0.265 ± 0.048 mg of DON; 0.013 ± 0.001 mg of zearalenone/kg), a low DON diet (1.68 mg of DON/kg; 0.145 ± 0.007 mg of zearalenone/kg), or a high DON diet (12.209 ± 1.149 mg of DON/kg; 1.094 ± 0.244 mg of zearalenone/kg). Increasing levels of DON decreased the weekly weight gain linearly (P ≤ 0.041) during the first 3 wk of exposure; there were no significant differences in the weight gain of the birds after wk 3. With increasing levels of DON, the titers against Newcastle disease virus increased linearly during wk 2 (P = 0.022) and wk 4 (P = 0.033) of exposure, whereas the titers against infectious bronchitis virus decreased linearly (P = 0.006) during wk 5 of exposure. The serum protein concentration increased linearly (P = 0.017) during wk 2 and quadratically (P = 0.002) during wk 4 of exposure. Under these experimental conditions, the performance and vaccine response of the broilers were modulated to varying degrees at concentrations of DON that are currently permitted (up to 5 mg/kg of diet) in many countries. Further studies are therefore required to clarify the implications of these results on the welfare of chickens.