The labor force participation rates of whites, blacks, and Spanish-Americans, grouped by sex, are explained in a linear regression model fitted with 1970 U. S. Census data on Standard Metropolitan Statistical Area (SMSA). The explanatory variables are: average age, average years of education, vocational training rate, disabled rate, unemployment rate, change in employment rate, wage rate, average nonlabor income, married rate, proportion of women with young children, wage social inequality, and unemployment social inequality. Wage social inequality is defined as the average wage rate of a specific racial or ethnic group in relation to the overall average wage rate, adjusted for skill differences between the group in question and the overall population. Unemployment social inequality is, analogously, the adjusted relative unemployment rates. (NTIS)