From January to June 1992, a large outbreak of cryptosporidiosis occurred in Jackson County, Oregon. Epidemiologic investigations associated 43 cases of cryptosporidiosis with the drinking water system in the small community of Talent, Oregon. Mechanical and operational deficiencies at one of the city's water filtration plants along with unusually poor raw-water supply conditions because of low stream flows were possible cocauses of the outbreak. Correction of the deficiencies in the filter plant resulted in substantial improvement in treated-water quality, and this improvement coincided with the end of the Talent-related outbreak. Includes 19 references, figures.