b1p4wich ELISAs, which use monoclonal antibodies for both the capture and the completion stages, were developed for the detection of verotoxins I and II (non-variant). The ELISAs were used to investigate the incidence of verotoxins in 304 samples of bovine faeces collected from cases of enteritis, and 113 samples collected from normal animals. For most samples, the tests were carried out directly on faeces, and on colony sweeps which were taken from cultures grown from the faeces. These colonies were either grown directly from faeces (mixed colony sweep) or from a coliform culture purified from this (purified colony sweep). All the positive ELISA reactions were investigated by Vero cell cytotoxicity assays for the confirmation of verotoxins. The largest numbers of ELISA-positive reactions which were confirmed by cytotoxicity assays were obtained with mixed colony sweeps. Verotoxin activity was confirmed in 74 (24 per cent) of the samples from cases of enteritis and from 35 (31 per cent) of the normal faeces samples. The occurrence of ELISA reactions unconfirmed by cytotoxicity assays and high cytotoxicity levels with low ELISA readings indicated the presence of non-toxic verotoxin epitopes and the presence of toxic verotoxin variants in the samples.