An enzyme immunoassay was developed which could detect sporidesmin in pasture samples. The assay had a linear working range of 0.4-40 ng/ml sporidesmin A while validation using pasture extracts gave mean percentage recoveries of 124% for samples containing 1 ng/ml sporidesmin and 97% for extracts containing 20 ng/ml sporidesmin. The sporidesmin levels and numbers of Pithomyces chartarum spores from many pasture samples were compared. The amount of sporidesmin detected generally corresponded to the number of spores found in the sample.