A vertical beam spectrophotometer for measuring the light absorption of an assay prepared using standard wet chemistry procedures and conventional solid phase coated bead technology is disclosed. The spectrophotometer measures the absorption of the assay in a conventional reaction cuvette with the bead remaining in the cuvette. The light source of the spectrophotometer illuminates the bead, which diffuses the light into the surrounding assay solution. A lense projects the diffused light onto a photocell which converts it into an electrical signal having magnitude related to the light absorption of the assay. The signal is processed in a known manner by conventional processing circuitry to obtain an absorption value.