Two fluoroimmunoassays for the specific detection of morphine in urine are described based on the use of ovine antibodies and fluorescein-labelled normorphine. The first, a polarisation fluoroimmunoassay, is performed by adding 10 microliter of urine to 1.5 ml of a single-reagent, comprising premixed antiserum and tracer, incubation for a few minutes at ambient temperature and measurement of fluorescence polarisation. The assay gives results which compare well with those by thin-layer chromatography, EMIT d.a.u., and the Boehringer opiate drug test. Although adequate for routine screening for drug abuse, the technique is not as sensitive as some radioimmunoassays. Therefore, a second fluoroimmunoassay was developed based on the use of the same antibodies covalently coupled to magnetisable particles to facilitate both the separation of the bound and free fractions and the removal of non-specific interfering substances. Thus, larger sample volumes could be employed and greater sensitivity achieved.