Inactivation of Cryptosporidium oocysts is a major challenge for water treatment facilities, many of which use conventional treatment for this purpose. Information on the removal efficiency of Cryptosporidium and potential surrogate parameters over a broad range of water quality and treatment conditions, however, is not readily available. Thus, water treatment facilities must resort to trial and error to arrive at the best combination of treatment processes to remove Cryptosporidium. In this study, 14 pilot-scale tests were performed to assess the ability of conventional treatment to control Cryptosporidium and three surrogates: turbidity, total particle counts, and aerobic endospores. The effects of coagulant type, coagulant dose, raw water quality, filter loading rates, and filter media were evaluated. Cryptosporidium removals were then compared with the removals of the three surrogates. The authors found that when coagulation is properly controlled, total Cryptosporidium removal improves by orders of magnitude, and total Cryptosporidium removal is greater than the total removal of turbidity, particles, or spores. The authors acknowledge that in general pilot-scale tests using higher Cryptosporidium concentrations than those found in full-scale conventional treatment plants also show higher Cryptosporidium removals. The study's conclusions, however, indicate that water treatment facilities may want to consider experimenting with different coagulants and coagulant doses to optimize coagulation and in the process improve Cryptosporidium removal. Finally, because the differences in pilot- versus full-scale removals may have serious regulatory and operational implications, Dugan and colleagues hope that the information in their article will provide the impetus for more rigorous coagulation control, the adoption of an inexpensive and simple test for spore enumeration, or the acquisition of online turbidimeters and particle counters. Includes 22 references, tables, figures.