1. Live body weight gain (WG) and food conversion efficiency (FCE) were measured over a 4-week period in chicks (female, Kabir strain), inoculated intragastrically at one week of age with either a single dose (1 ml) of 10(7) live bacterial cells of Lactobacillus fermentum (LBF) or a strain of Lactobacillus spp. (LB), named Autruche 4 (A4), suspended in 1 ml of phosphate-buffered saline (PBS, pH 7.0); controls (n = 10) were inoculated only with PBS. The same commercial chicken feed was used throughout the 4-week experiment. 2. Compared with the control group, WG to 8 and 21 d, and also liver weight, were significantly greater in LBF and A4 treatments and FCE improved in both of the experimental groups. Compared with the A4 treatment group, WG was significantly higher and FCE improved in the LBF-treated group. The effects of A4 treatment on chicks were similar to those in an earlier pilot experiment using the same methodology but with 1-week-old female chicks (Kabir) inoculated with either the A4 strain or strain of LB named Autruche 5. 3. It is concluded that a single dose of Lactobacillus fermentum or Lactobacillus spp. (Autruche 4) administered intragastrically improves WG and FCE of broiler chicks.