A computer-based expert system will be designed and implemented to aid cytopathology laboratories in the diagnosis of cervical cancer and its precursor lesions. The diagnostic software and its built-in quality control may reduce diagnostic errors and prevent overtreatment of patients; both are problems especially in the operation of laboratories with modest workloads, and thus lack of experience. Such laboratories handle 80% of all cancer prescreening in the United States. The system will offer guidance by dialogue based on material developed by the International Academy of Cytology, and the Tutorials of Cytology, micromorphometric assistance based on results from quantitative and analytical cytologic research, computer-graphic aids, image data bases and patient data bases, to serve as references and for a self-training, continuing education process.