Abstract: Para-amino-salicylic acid (PASA) or a water-soluble salt thereof, e.g. of an alkali metal, alkaline earth metal, ammonia or an amine is used for the stabilization of the enzymatic activity of peroxidase in aqueous medium. The stabilizing agent may be in the form of an aqueous solution compatible with peroxidase medium in which PASA or its salt is dissolved in a quantity efficacious for stabilization, preferentially comprised between about 8 .mu.g/ml and about 2000 .mu.g/ml of the solution based on PASA. With such stabilizing agent, one can efficaciously stabilize solutions of peroxidase, whether free or conjugated to immunological carrier reagents, and prepare these reagents in advance in a diluted form ready for use.

Abstract: An interspecific antigen of Mycobacteria consists essentially of a mixture in substantially immunochemically pure form of a protein having a molecular weight of at least about 4.times.10.sup.6 Daltons and polysaccharide having a molecular weight of at least about 1.times.10.sup.6 Daltons, and has when subjected to cross-electrophoresis an immunoelectrophoretic precipitation pattern corresponding to A60-antigen of Mycobacteria bovis strain BCG. This antigen is effective for detecting the prior exposure of a subject to Mycobacterial infections by a cutaneous test.

Abstract: A 60-like antigens isolated in a one-step reaction from the bacterial cytoplasma of Mycobacteria are useful for the production of diagnostic tests.

Abstract: The sensitivity of hemagglutination inhibition tests is improved by introducing a determined amount of lyophilized antigen or antibody into serological tubes in the absence of the indicator component. The test fluid to be analyzed is incubated solely in the presence of its binding partner in a liquid phase. After completion of the binding reaction (about 5 hours but extendable to 18 hours), the sensitized indicator solid phase, usually consisting of sensitized red blood cells, is added. By this process a 10 to 20 fold increase in sensitivity of the hemagglutination inhibition test is routinely achieved.