In each of three 2-wk experiments, chicks were inoculated on d 9 or 11 with 5.0 x 10(5) Eimeria acervulina sporulated oocysts (acute infection) or on d 9, 12, 15, and 18 with 1.5 x 10(5) sporulated oocysts (chronic infection). In Experiment 1, both fish meal (15%) and GroBiotic-P (GB; International Ingredient Corporation, St. Louis, MO; 5%) diets completely ameliorated the negative effects of acute and chronic coccidiosis infection on growth performance of crossbred chicks. The acute coccidiosis infection greatly reduced MEn and amino acid (AA) digestibility, and the magnitude of response varied with the timing of excreta collection after inoculation. Both fish meal and GB diets ameliorated the large negative effects of coccidiosis infection on MEn and AA digestibility. In Experiment 2, a wheat-barley-pectin diet and acute coccidiosis infection depressed crossbred chick BW gain, AA digestibility, and MEn in comparison with a corn-soybean meal diet; there generally were no interactions between diet type and coccidiosis infection. In Experiment 3, using commercial broiler chicks, diets containing 2 to 6% GB did not improve the growth performance of coccidiosis-infected chicks, but they did improve the growth of the noninfected chicks. The results of this study indicate that coccidiosis infection (E. acervulina) reduces MEn and AA digestibility in chicks and that the coccidiosis effect is influenced by diet composition, type of infection (acute vs. chronic), and timing of excreta collection.