The technique of immunoblotting (Western blotting), following separation of proteins by gel electrophoresis, is widely used in molecular and cell biology (1, 2). It enables the proteins under study to be fixed on a membrane that is much easier to handle and probe than a polyacrylamide or agarose gel. Proteins are then detected by incubation of the membrane with an appropriate primary antibody for the protein concerned, followed by incubation with a secondary antibody raised to recognise epitopes on the constant region of the primary antibody. This secondary antibody can be conjugated to a radio-label, a fluorophore or an enzyme (3). In the latter case an appropriate substrate is then used to generate a product which can be measured. Early workers used radiolabels, particularly 125I, to detect proteins on immuno-blots (1). The sensitivity was good and the method gave a quantifiable permanent record in the form of an image on X-ray film. However long exposure times were needed and this, combined with the associated safety and disposal problems, has made the technique less popular. Fluorescently-labelled antibodies have also been employed using a fluorescent laser scanner for measurement (4). This system overcomes the problems of dealing with radio-active materials and has the advantage that the signal is read directly from the bound antibody but has limits in terms of sensitivity (5). Enzymes conjugated to secondary antibodies offer a detection system where many molecules of product are generated for each enzyme-linked molecule of antibody bound to protein. This achieves amplification of the signal, giving increased sensitivity, without the need for the special handling conditions associated with radioactive tracers.