The objective of the experiment was to study the influence of lactose, inulin, and modified β-glucan as additives to maize-based diets on the performance of broiler chickens, as well as on the pH in the crop, gizzard, ileum, caeca and on populations of selected ileal microflora species. Over the entire experimental period (day 1 - day 42), the animals (384 male broilers, 4 treatments, 12 replicates of 8 birds per treatment) were offered maize-based diets. The diets were fed either without any supplementation (control diet), or with a supplement of either 0.025% modified β-glucan, 0.3% inulin, or 0.2% purified lactose. Body weight gain decreased (P<0.05) and feed conversion ratio worsened (P<0.05) in birds fed diets with supplements in comparison with the nonsupplemented control group. The counts of lactic acid bacteria in ileal digesta were lower (P<0.05) in birds supplemented with lactose. No difference between the dietary treatments was observed regarding the population of intestinal coliform bacteria.