Research has shown that methionine+ cysteine (M+C) requirements may be higher when chickens are infected with Eimeriaapp. In a 4 × 2 factorial design, broilers (11 to 21 D) were fed one of 4 corn–soybean meal-based diets containing either 0.6, 0.8, 0.9, or 1.0% standardized ileal digestible (SID) M+C; on day 14, broilers from each diet were gavaged with either phosphate-buffered saline (PBS) or a commercial coccidiosis vaccine (at 100 × vaccine dose) which provide a mixture of live Eimeria acervulina, Eimeria maxima, and Eimeria tenellaoocysts. Growth performance was recorded from day 11 to 21. Plasma and intestinal luminal samples were collected on days 14 and 21. Intestine lesion scores and fecal oocyst counts were conducted on day 21. Regardless of dietary SID M+C levels, compared to PBS gavaged broilers, the Eimeria-challenged broilers had (1) decreased (P< 0.05) body weight gain (BWG), feed intake (FI), and gain-to-feed ratio (G:F); (2) increased (P< 0.05) intestinal lesion scores and fecal oocyst counts; (3) increased (P< 0.05) plasma anti-EimeriaIgG, and intestinal luminal total IgA and anti-EimeriaIgA concentrations; and (4) increased (P< 0.05) levels of duodenum luminal gamma interferon (IFN-γ) and interleukin-10 (IL-10), as well as jejunum and cecum luminal IFN-γ concentrations. Regardless of Eimeriachallenge, when compared to 0.6% SID M+C, broilers fed ≥0.8% SID M+C had (1) increased (P< 0.05) BWG, FI, and G:F and (2) increased (P< 0.05) levels of jejunum luminal total IgA. After Eimeriachallenge, broilers fed 0.8% SID M+C had increased (P< 0.05) levels of jejunum luminal anti-EimeriaIgA compared to broilers fed diets containing 0.6 and 1.0% SID M+C. Collectively, in 11- to 21-D broilers, the growth suppression caused by Eimeriainfection could not be mitigated by further increasing dietary M+C alone ≥0.8%. Further research should investigate interactions between dietary M+C and other nutrients for support of immune function and growth in pathogen-challenged broilers.