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 (>3 log[10] reportable). The combination of experiments with both medium-pressure and pulsed-UV systems showed, with a 95-percent statistical confidence, that UV doese of 7.6 and 11 mJ/cm[2] would, respectively, result in 1- and 2-log[10] inactivation of C. parvum. Includes 17 references, tables, figures.