Abstract: Detection of bindable substances such as antibodies and antigens using enzyme linked immunosorbent assays having particular utility in home diagnostic applications. The preferred implementation of the invention is characterized by the steps of admixing a sample suspected of containing the bindable substance to be detected with an antibody-enzyme conjugate, immersing an antibody coated solid support into the mixture and then exposing the coated support to an activated chromogenic solution. The conjugate for use in the home diagnostic assay is preferably contained within a lyophilized mixture. The lyophilized mixture contains components which preserve the antibody-conjugate's reactivity and immunologic binding specificity even if the lyophilized mixture had been subjected to hot, humid environmental conditions. Active components in the lyophilized mixture include polyethylene glycol, sugars, and surfactant.