Two fluoroimmunoassays have been developed for the detection of cannabinoids in urine. They employ a specific ovine antiserum and a fluorescein-labelled analogue. The first was a single-reagent polarisation fluoroimmunoassay which, because of its simplicity, was easy to automate and suitable for the screening of large numbers of samples but which had limited sensitivity.For greater sensitivity a second fluoroimmunoassay was designed, based on the use of antibodies covalently coupled to magnetisable particles. Owing to the large sample volume that could be assayed and the ability to remove all non-specific interfering factors during the separation step, this separation assay was at least 100 times more sensitive than the polarisation fluoroimmunoassay.