Cancer mortality during 1970-85 of immigrants from East and West Africa and the Caribbean to England and Wales is described. Overall cancer mortality was raised in West African males (RR 1.38, 95% CI 1.25-1.54), and non-significantly raised in West African females (RR 1.14, 0.96-1.37) compared to mortality in the England and Wales-born population. Much of the increased risk was due to very high rates of liver cancer in males (RR 31.6, 23.8-41.9), but rates were also raised for a wide range of other cancers in each sex. Only lung and brain cancer had significantly decreased mortality. In East Africans, overall cancer mortality was low in males (RR 0.63, 0.56-0.70), and in females (RR 0.80, 0.72-0.89). Mortality was significantly low for cancers of the stomach, pancreas and testis, and Hodgkin's disease in males, for cervical cancer in females, and for lung cancer and melanoma in both sexes. Cancer sites with significantly raised mortality included oropharyngeal cancer, leukaemia, and multiple myeloma in both sexes. In Caribbean immigrants overall cancer rates were significantly low in males (RR 0.71, 0.68-0.74) and in females (RR 0.76, 0.73-0.80). Mortality was significantly low for many cancers including colorectal, lung, testis and brain cancers. Mortality was significantly raised only for cancer of the prostate in males, of the placenta in females, and of the liver, non-Hodgkin's lymphoma and multiple myeloma in both sexes. Overall, mortality was high from prostatic cancer and liver cancer, and was low from brain cancer, in predominantly ethnic African immigrant groups. Both East and West African immigrants had raised rates of leukaemia. All of the migrant groups had high rates of multiple myeloma and low rates of testicular, ovarian and lung cancer. Genetic and environmental factors that may contribute to these patterns are discussed.