Bench-scale experiments were conducted to determine the germicidal effects of polychromatic (200 to 300 nm) ultraviolet (UV) radiation on Cryptosporidium parvum oocysts. C. parvum oocysts (between 10[4] and 10[6] oocysts/mL) were suspended in treated surface water and irradiated with medium-pressure and pulsed-UV light. UV doses were determined by radiometer and joulemeter, respectively. Oocyst inactivation was based on infectivity reduction using a human cell-culture assay (reverse-transcriptase polymerase chain reaction [RT-PCR] with quantitation of gel electrophoresis by densitometry). Initial pulsed-UV experiments showed that UV doses of 16 mJ/cm[2] or more provided complete inactivation of C. parvum stock (