Two experiments were conducted to characterize the toxicity and evaluate the efficacy of alum to increase intestinal strength in young broiler chicks. Cobb x Cobb male broiler chicks were placed in an experimental design consisting of six dietary treatments of alum (control, 0.23, 0.47, 0.93, 1.9, and 3.7%) with four replicate pens of 10 broilers per pen. The chicks were housed in electrically heated batteries and provided the treatments for ad libitum consumption from 1 d to 3 wk of age. Alum significantly (P < or = 0.05) decreased body weights at 1.9 and 3.7% in Experiment 1 and at 0.93, 1.9, and 3.7% in Experiment 2. Feed conversion and the relative weight of the gizzard were increased in both experiments at 3.7%. Serum phosphorus was decreased at 1.9 and 3.7% in Experiment 1 and at 3.7% in Experiment 2. Intestinal and bone strength were decreased in both experiments at 3.7%. Bone ash was reduced at 3.7% in Experiment 2, bone S levels increased at 1.9 and 3.7% in Experiment 1 and at 3.7% in Experiment 2, and bone Al levels were elevated in both experiments at 3.7%. Muscle levels of P and S decreased, and that of Ca increased at 3.7%. Aluminum levels were not elevated in muscle tissues. These data indicate that alum can be toxic to young broiler chicks, but at levels that would not be expected to be reached through litter consumption, and that alum did not increase intestinal strength.