An apparatus and method for automated assay of biological specimens positioned on microscope slides. The apparatus comprises an interactive optical subsystem for viewing the biological specimen on the slide and for producing an interactive video signal corresponding to the viewed image. An automated optical subsystem includes a single high power microscope objective for scanning a rack of slides, portions of which having been previously identified for assay in the interactive optical subsystem. The system also includes a processor for processing the interactive and automatic video signals from the two optical subsystems. The processor receives the automatic video signal and performs biological assay functions upon it.