Abstract
Epifluorescent microscopy and flow cytometry were used in different combinations with fluorescein isothiocyanate-labeled immunoglobulins M and G3 to estimate the numbers of Cryptosporidium parvum oocysts in soil extracts containing 10 to 10,017 oocysts/ml. No combination had a systematic effect on accuracy or precision. Background debris may have produced overestimates at low oocyst concentrations when flow cytometry was used.