The Prostate, Lung, Colon-rectum and Ovary Cancer Screening Trial is designed to determine in screenees aged 60-74 years at_entry_ whether: a. In females and males (1) screening with flexible sigmoidoscopy (60 cm sigmoidoscope) can reduce mortality from colo-rectal cancer; and, (2) screening with chest x-ray can reduce mortality from lung cancer. b. In males (1) screening with digital rectal examination plus serum prostate-specific antigen (PSA) can reduce mortality from prostate cancer; C. In females (1) screening with pelvic examination plus CA 125 and transvaginal ultrasound can reduce mortality from ovarian cancer; The secondary objectives are: (1) to assess screening variables other than mortality for each of the interventions including sensitivity, specificity, and positive predictive value; (2) to assess incidence, stage, and survival experience of cancer cases and (3) to investigate the mortality predictive value of biologic and or prognostic characterizations of tumor tissue as intermediate endpoints. This contractor will recruit and randomize to screening or control 15,000 subjects in equal gender balance. Screening will be annual for four years, except that sigmoidoscopy will be dome only in the initial and last screen. Subjects will be followed for ten years from entry. A total of 148,000 subjects will be recruited by ten participating Screening Centers. The trial also includes a Data Management and Coordinating Center and a Laboratory for blood assays.