A method for the rapid quantitative analysis of dot blot assays is presented. A video camera, an NTSC compatible frame grabber board, and an AT personal computer are used to read photographic exposures of the assay plate. Image processing and image analysis techniques are used to calculate the orientation of the dot raster and then to compensate for the effect of variations in field illumination on measurements of local contrast. Local contrast (between dots and background) is an exponential function of the amount of hybridization between blotted DNA and complimentary oligonucleotide probes. The amount of hybridization between blotted DNA and oligonucleotide probes of known sequence is the criteria used to establish HLA-DR tissue types. Although the assay described here utilizes a chemiluminescent reaction, this algorithm may be used to read any assay that produces a rectangular raster of dots.