Three projects were presented to demonstrate the types of intervention that should occur in high risk groups for disease: the Augusta, Georgia chemical workers bladder cancer project; the nationwide Pattern Makers' League of North America colorectal cancer project; and the Port Allegany, Pennsylvania flint glass workers lung cancer project. The objective of these projects was to provide a comprehensive response for each high risk group. Study I involved 1,094 predominantly black, male workers who faced an estimated four fold increase in relative risk for bladder cancer due to workplace exposure to beta-naphthylamine (91598) between 1949 and 1972. Study II involved almost entirely white males, highly skilled, and well paid, who were shown by three independent epidemiological studies to have possibly a doubled risk of mortality from colon and rectal cancers. Study III involved approximately 1,200 almost exclusively white males at high risk of developing cancers associated with workplace exposure to asbestos (1332214) between 1964 and 1972. Programs were evaluated on the basis of participation and compliance rates. In Study I, the overall participation rate was 88 percent, and the compliance rate was 73 percent. In Study II, the overall participation rate was 48 percent, and the compliance rate was 94 percent. In Study III, the overall participation rate was 70 percent. In Study I, five cases were identified as a result of the screening program. In Study II, 12 cases of colorectal cancer have been confirmed, and 219 pattern makers were found to have colorectal polyps. In Study III, the first case of lung cancer, which has a 20 year latency period, was detected through the program in 1983. The authors conclude that much etiological and basic biomedical knowledge can be derived from intervention demonstration projects. Highly targeted intervention approaches are possible.