Congenital toxoplasmosis is rarely diagnosed in Colorado. To better determine whether this was the result of under-reporting or a valid observation, the sera of 120 consecutive prenatal patients from a lower-income clinic population were tested for antibodies to Toxoplasma gondii. Four of the patients had positive Sabin-Feldman dye tests, for a 3% incidence of past infection. None had immunoglobulin M (IgM) antibody. This rate is considerably lower than that in other populations, perhaps because the high-altitude, arid environment shortens oocyst survival in soil. A questionnaire designed to detect risk factors for Toxoplasma infection, such as exposure to cats or undercooked meat, did not indicate any differences between the antibody-positive and antibody-negative groups.