The effects of feeding diets containing sunflower and wheat middlings pre-treated with fibre-degrading enzymes were investigated. Based on hatch body weight (BW), 288 Ross-708 male broiler chicks were placed in cages (six birds/cage). Diets were: 1) positive control (PC), a maize–soybean positive control; 2) negative control (NC), PC plus untreated sunflower meal (USM) and wheat middlings (UWM); and 3) four test diets in which USM and UWM were replaced with pre-treated sunflower (TSM) and wheat middlings (TWM) at 25% (NC25), 50% (NC50), 75% (NC75) and 100% (NC100). The pre-treated feedstuffs were mixed with 1% of FDE in a ratio of 1:2 w/w for feedstuff:water and incubated for 24 hours at 40 °C, and oven-dried before feed preparation. Diets were formulated for two phases (starter, 0–21 d) and finisher (22–42 d). Diets were allocated in a completely randomized design (eight replicates per diet) and birds had free access to feed and water. Bodyweight (BW) and feed intake (FI) were monitored by phase, and one bird per cage was sacrificed on days 21 and 42 for samples. The BW and BW gain (BWG) of NC up to NC50 were not different relative to PC, but NC75 and NC100 were lower than PC throughout the study. On day 21, liver weight had increased linearly and on day 42, tibia length and diameter linearly decreased with the inclusion of TSM and TWM. In conclusion, TSM and TWM at low levels did not affect performance while high inclusion levels reduced the performance of the broilers.