The objective of this study was to develop a microscopic method using internal movement of Cryptosporidium parvum oocyst as an indication of potential viability, that is rapid, easy and reproducible for possible use in pilot plants and seeded studies. This method would not require the need for expensive, hazardous chemicals, and no great investment of time or technical skill. Ten microliters(ul) of freshly purchased Cryptosporidium parvum was pietted onto a single well of an Erie Scientific Co. two well slide. A Fisher-Finest Premium Cover glass coverslip for two wells was placed on the slide, and then the slide was sealed with clear nail polish. This procedure was repeated for three more slides. Each of the four slides was held at a different temperature. Slides were initially allowed to sit for two hours, and then observed for oocyst activity. Includes 10 references.