Four-week-old Single Comb White Leghorn male chicks were infected with 1,000,000 sporulated oocysts of Eimeria acervulina, or with 50,000 sporulated oocysts of E. necatrix, or with 50,000 sporulated oocysts of E. brunetti, or with 50,000 sporulated oocysts of E. tenella, or were left uninfected as the controls. On Days 1, 3, 6, 10, 14, 21, and 28 following the infection, 5 birds from each group were randomly selected and administered 2.0 microCi of 54Mn orally. At 1, 2, and 4 hr after administration of the radiotracer, the amount of radioactivity appearing in the bloodstream was measured. The absorption of manganese 6 days after the beginning of the E. acervulina infections was decreased to 23 to 34% of that in the uninfected birds, whereas E. necatrix infections resulted in a smaller and more variable decrease in manganese absorption. The other coccidial infections did not decrease manganese absorption significantly. On the 14th day of the infections, all four coccidial infections increased manganese absorption two- to fourfold that found in the controls in one trial but not in the second trial. At other times during the coccidial cycle, no effects were seen on manganese absorption.