The effect of 2 different blends of essential oils on Clostridium perfringens (Cp) in the intestine and feces of broiler chickens was tested in 6 field trials for each blend. One hundred parts per million of the blends were mixed in a commercial corn-based diet throughout the entire growing period for experimental flocks. Samples from the jejunum, cecum, cloaca, and feces were taken on d 14, 21, and 30 from experimental and control flocks and tested quantitatively for Cp via blood agar plate, litmus milk medium, and ELISA. Blend A reduced (P < or = 0.05) the average Cp concentration in the feces on all sampling days, in the jejunum and cecum on d 14 and 21, and in the cloaca on d 14. Blend B effected a significant reduction of Cp concentration in the jejunum on d 14 and 30 and in the cloaca on d 14. The percentages of specimens from the control group that tested positive for Cp were 83.3% for feces, 88.0% for jejunum and cloaca, and 82.6% for cecum. Specimens from the feces and 3 sections of the intestine were Cp positive in groups treated with blend A (60.8, 64.6, 47.9, and 70.8%) and with blend B (65.9, 63.6, 63.6, and 72.7%). Our results indicate that specific blends of essential oil components can control Cp colonization and proliferation in the gut of broilers and therefore may be of help to prevent problems with Cp and necrotic enteritis.