Knowledge of cancer prevention and control was defined in terms of prevention, etiology, treatment, symptoms, cancer rates, screening, and detection examinations. A survey of 86 African Americans and 68 white Americans in Alameda County, California was completed in 1985. An index comprised of 69 knowledge items was assessed. A multivariate analysis of race, education, socioeconomic status, and occupation confirmed that these characteristics were independent predictors of knowledge. Blue collar work status was the most important predictor of low knowledge levels. African Americans were less knowledgeable than white Americans with regard to diet in preventing cancer and treatment modalities for cancer, and were most likely to perceive surgery as contributing to metastases. Low education and income status predicted low levels of knowledge. An important consideration in changing knowledge levels is the need to translate technical information about treatment and metastases in ways that are effective in reaching target populations at risk for low levels of knowledge. Cancer prevention and control programs need to develop materials and strategies that are responsive to communities whose members are predominantly African Americans or blue collar workers, or have low levels of education and income.