We describe a rapid immunochromatographic method for the quantitation
of progesterone in bovine milk. The method is based on a 'competitive'
assay format using the monoclonal antibody to progesterone and a prog
esterone-protein conjugate labelled with colloidal gold particles. The
monoclonal antibody to proges terone is immobilized as a narrow detec
tion zone on a porous membrane. The sample is mixed with colloidal gol
d particles coated with progesterone-protein conjugate, and the mixtur
e is allowed to migrate past the detection zone. Migration is facilita
ted by capillary forces. The amount of labelled progesterone-protein c
onjugate bound to the detection zone, as detected by photometric scann
ing, is inversely proportional to the amount of progesterone present i
n the sample. Analysis is complete in less that 10 min. The method has
a practical detection limit of 5 ng of progesterone per mi of bovine
milk.