An improved polymerase chain reaction (PCR)-based method for determining the species composition of Eimeria in poultry litter was developed by incorporating species-specific internal standards in the assay. Internal standard molecules were prepared by fusing seven different Eimeria species-specific intervening transcribed sequence 1 (ITS1) rDNA primer pairs to a non-Eimeria DNA molecule and by cloning the hybrid DNA molecules into a plasmid. The internal DNA standards were then used in Eimeria-specific ITS 1 PCR, and they were found to be capable of detecting E. acervulina, E. maxima, E. praecox, and E. tenella oocysts isolated directly from poultry litter.