The volume and quality of the water filtered greatly influenced the overall recovery of the method. Increased organic matter and sediment more than likely interferes with recovery of the oocysts from the filter, recovery after sheather's flotation and detection. Still it is significant that naturally occurring Cryptosporidium could be isolated from secondary effluent using this method and rough estimates gave a concentration of five to 17 oocysts per liter. This recent finding illustrates the necessity for further investigation of Cryptosporidium. Further improvements are needed for filtration-elution method for concentration of Cryptosporidium oocysts.