Ascaris, hookworm, Strongyloides, the tapeworms, and the protozoans Giardia lamblia and Entamoeba histolytica form the majority of gastrointestinal parasites that have clinical significance in the United States. Of these, roundworms (e.g., Ascaris, Strongyloides, and Trichinella) typically are accompanied by peripheral blood eosinophilia. Diagnosis usually depends on examination of the feces for larvae or eggs. There is always a question regarding how many stool specimens should be obtained. One literature review citing studies before 1960 states that a single “ova and parasites” (O&P) specimen detected only 35%-50% of pathogens. Another in 1984 found 83% in the first specimen and 12% in the second. A study in 1989 and another in 1992 detected 90% in the first specimen. The results would be influenced by factors such as whether specimen concentration, stained permanent slides, purged or nonpurged specimens, and parasitologist or nonspecialist examination were performed. In most situations, standard recommendations state that three routine stool specimens, collected one every day and sent for ova and parasites examination is adequate (Giardia and E. histolytica may require more, if the initial specimen is negative). According to one report from a specialized parasitology laboratory, a single specimen obtained after use of magnesium sulfate cathartic detected about 80% of the most important parasites that were eventually detected using multiple specimens. The average laboratory would probably not obtain this degree of proficiency.