Cardiovascular disease mortality rates have fallen dramatically in blacks in the United States. To determine whether this may be due to a decline in cardiovascular risk factors, we compared risk factors in a 1985 urban black population, ages 35 to 69, with those obtained in blacks of the same area in 1973-74. Age-adjusted mean body mass and the prevalence of overweight increased significantly over the 12-year period in both men and women. Mean systolic blood pressures declined significantly in both sexes, diastolic blood pressure declined significantly in men, and the proportion of men and women hypertensives on medication and under control increased. The overall prevalence of cigarette smoking changed very little, but the proportion of heavy smokers decreased significantly in men. No significant changes occurred in resting heart rate. Concurrently with these risk factor trends, age-adjusted heart disease mortality rates in area blacks fell 27% between 1968-73 and 1979-84, and stroke mortality fell 58%. Changing risk factors may be contributing to declining cardiovascular mortality rates in blacks. However, overweight seems to be a worsening problem.