Monensin was effective within the range 60-100 p.p.m. in control of coccidiosis in turkey poults in a series of laboratory experiments. Under conditions of heavy infections with Eimeria meleagrimitis and E. adenoides, 100 p.p.m. of monesin was significantly more effective than 60 p.p.m. in protecting weight gains. When light or moderate infections with E. meleagrimitis, E. adenoides and E. gallopavonis were used, there were no significant differences among monesin-medicated treatments. In all instances the monensin-medicated treatments gained significantly more weight than noninfected, nonmedicated controls, when measured at 7 days post-inoculation. Similarly, oocyst, passage was reduced, feed conversion was protected and mortality was controlled in monensin-treated poults.