Two-week-old broiler chickens were inoculated orally with various doses of avian Eimeria that infect different sections of the intestine. The coccidia used were E. acervulina (duodenum), E. maxima (jejunum), E. brunetti (ileum) and E. tenella (caecum). The measurements evaluated were weight gains, intestinal lesion scores and changes in serum alkaline phosphatase (SAP) activity 6 days after infection. SAP activity was inversely proportional to both oocyst dose and gross intestinal lesion score, and directly proportional to weight gains with infections of E. acervulina, E. maxima and E. tenella. However, no significant changes in the SAP activity were found in those birds infected with E. brunetti. Taken together, the data suggest that SAP activity may be a sensitive marker of the pathogenesis of certain coccidial infections, especially in the duodenum, jejunum and caecum, that may be used as an additional factor in evaluating coccidial control measures.