Homicide rates from 1967 to 1971 were abstracted from World Health Organization records. Gini coefficients (indication of the degree of overall income inequality of a nation) were obtained from The World Bank Compilation of Data on Personal Income Distribution. Ethnic-linguistic frationalization was measured by a combined index of ethnicity and language developed by Rae and Taylor (1970) and reported in The World Handbook of Political and Social Indicators. Data were also obtained on economic production level, population density, labor force participation, and proportion of youth. Analyses indicate that vertical social differentiation, as measured by income inequality, and horizontal differentiation, as indexed by ethnic heterogeneity, have significant main effects on cross-national homicide. Evidence also suggests an interaction effect of inequality and heterogeneity on homicide. Increased ethnic heterogeneity apparently exacerbates the impact of income inequality on homicide rates. 3 tables, 2 figures, 30 references. (Author abstract modified)