An improved model was evaluated for determining the efficacy of salinomycin (or other anticoccidials) against severe coccidiosis in floor-pen-reared broiler chickens. Broilers were isolated in wire-floored starting batteries until they were 14 days old, then placed in floor pens and exposed to Eimeria spp. from two sources: litter heavily contaminated with three to eight cycles of coccidia-infected seeder birds, and feed contaminated with oocysts. This procedure resulted in an average mortality rate of 49.3% due to coccidiosis, and evidence of disease was present in all unmedicated birds examined. High lesion scores, depressed weight gains, and poor feed conversion were also observed. Salinomycin, 60 ppm, was efficacious against various mixed species infections in this model.