The protective effect of hyperimmune IgY fraction of egg yolk prepared from hens hyperimmunized with multiple species of Eimeria oocysts on experimental coccidiosis was evaluated in young broilers. Chickens were continuously fed from hatch with a standard diet containing hyperimmune IgY egg yolk powder or a nonsupplemented control diet and orally challenged at d 7 posthatch with 5.0 x 10(3) sporulated Eimeria acervulina oocysts. Body weight gain between d 0 and 10 and fecal oocyst shedding between d 5 and 10 postinfection were determined as parameters of protective immunity. Chickens given 10 or 20% hyperimmune IgY egg yolk powder showed significantly increased BW gain and reduced fecal oocyst shedding compared with control birds fed the nonsupplemented diet. In another trial, lower IgY concentrations (0.01, 0.02, and 0.05%) were used to treat birds with 1.0 x 10(4) oocysts of E. acervulina. Total oocyst shedding was significantly (P < 0.05) reduced in chickens fed the 0.02 and 0.05% hyperimmune IgY supplemented-diets compared with animals fed the nonsupplemented diet. Similarly, chickens fed 0.5% of hyperimmune IgY egg yolk powder diet and challenged with 1.0 x 10(4) oocysts exhibited reduced oocyst shedding compared with the control birds given 0.5% of IgY from nonimmunized hen eggs, although BW gain was not affected. We conclude that passive immunization of chickens with anti-coccidia IgY antibodies provide protective immunity against coccidiosis challenge infection.