EPA Method 1623 has been implemented as the standard protocol for the detectionof Cryptosporidium parvum and Giardia lamblia in water. This research focuses on the evaluation of the concentration and elution steps of EPA Method 1623 and their possible effects on the infectivity of Cryptosporidium parvum oocysts. Cell culture (FDM-MPN) was used to determine the infectivity of seeded infectious C. parvum oocysts in finished and surface water samples before and after processing. Preliminary results suggest that the concentration and elution steps in this method do not alter the infectivity of the oocysts. Includes 9 references, table, figure.