The anticoccidial activity of the ionophorus antibiotic narasin was tested against six species of coccidia (Eimeria acervulina, Eimeria mivati, Eimeria maxima, Eimeria necatrix, Eimeria brunetti, and Eimeria tenella) in battery-raised broilers. Feeding ration medicated with 60, 80, or 100 ppm narasin significantly improved weight gains during the periods of D 0 to D7 and D 0 to D 14 (D 0 = day of inoculation with sporulated oocysts), compared with the weight gains in corresponding inoculated groups fed unmedicated feed. A similar protective effect of the medication was seen with feed conversion ratios (feed consumed/bird weight) and coccidiosis-induced mortality. With most species studied, 40 and 60 ppm narasin was not as efficacious as 80 or 100 ppm. The maximum numerial improvement in weight gain and feed conversion ratio was with 80 ppm narasin. Gross intestinal lesion scores were reduced by medication compared with the scores in birds fed unmedicated feed. The overall trend was for a larger reduction in lesion score with higher drug levels. Narasin at 80 or 100 ppm was generally more effective in controlling individual or mixed species infections of coccidia than 99 ppm monensin.