The efficacy of β-cyclodextrin against experimental Cryptosporidium parvum infection was evaluated in neonatal lambs. The animals were treated by oral administration of the drug at 1 g/kg of body weight during 3 consecutive days. Preventive treatment was started within 1 day of birth, and therapeutic treatment was initiated at the onset of diarrhea following confirmation of infection. Disease development and drug efficacy were evaluated by monitoring the presence or absence of diarrhea and oocyst shedding from birth until 30 days of age. Weight gains at 15 and 30 days of age were also recorded. β-Cyclodextrin was highly effective as a prophylactic treatment; 1 animal did not acquire the infection, diarrhea was prevented in infected animals, and there was a considerable decrease in oocyst shedding. The therapeutic treatment was effective in decreasing the severity of diarrhea and the duration of oocyst shedding. The animals tolerated the drug well, and there was a significant increase in their body weights.