The in vitro interferon-gamma production by peripheral blood mononuclear cells and the local antibody build up was monitored in neonatal calves experimentally infected with Cryptosporidium parvum and in negative controls of the same age. From day 6 p.i. on, an infection-induced interferon-gamma response was observed in lymphocyte cultures after stimulation with Cryptosporidium oocyst antigen preparation. Only the Cryptosporidium-infected calves developed local IgA and IgM responses from day 6 p.i. on, with peak values at day 10 p.i. These antibodies disappeared quickly, perhaps due to the strict hygienic measures and consequently the absence of a continuous antigenic stimulation.