Noting the dearth of accurate information regarding the quality and quantity of Cryptosporidium oocysts used for experimentation, the authors used isolates meeting stringent quality assurance criteria to document the variation of results with three different enumeration techniques -hemacytometer, cellulose-acetate membrane, and well slide. In 70 comparisons of the three techniques, results generated by well slide and hemacytometer varied by an average of 24.7 percent, hemacytometer and membrane results varied 67.6 percent, and well slide and membrane results varied 79.3 percent. Significant discrepancies between counts generated by different techniques indicate a strong probability of poor accuracy in previous enumeration based studies. Recovery of oocysts after Percoll-sucrose flotation varied considerably with either hemacytometer or membrane counting techniques, which helps explain low precision with the Information Collection Rule protozoan method. Incomplete description of experimental procedures hinders Cryptosporidium research directed toward improving the analytical method, evaluation of water treatment efficacy, and surrogate development. Includes 10 references, figures.