To optimize routine screening for cryptosporidiosis, 198 stool samples from patients at risk and from calves were examined by enzyme immunoassay (EIA), a direct fluorescent-antibody (DFA) and a modified immunofluorescence assay. Ninety-nine samples were positive in at least one assay, whereas 99 were negative in all three assays. Sensitivity of antigen EIA and DFA were similar (94%, 95% CI: 88-98%, and 91%, 95% CI: 84-95%). The modified immunofluorescence was significantly less sensitive (64%, 95% CI: 55-74%). 149 samples were also examined by two nested PCR assays targeting either the 18S rRNA or Cryptosporidium outer wall protein (COWP) gene. A PCR product was amplified from 86 out of 89 samples being positive in at least one other assay (sensitivity 97%, 95% CI: 91-99%). None was obtained from 60 samples negative in the three other assays. PCR assays did not increase the detection rate. Antigen EIA or DFA appear sufficient for routine Cryptosporidium screening of fecal samples.