Nationwide rates of death from systemic lupus erythematosus (SLE) were estimated from National Center for Health Statistics mortality data for 1968 to 1972 according to age, sex, and race. The overall rates for females, 6.3 per million person-years (whites 5.2, blacks 14.8), were about four times that for males, 1.6 per million person-years (whites 1.5, blacks 2.2). The overall rate for blacks, 8.8, was 2.6 times that for whites, 3.4. An earlier rise in age-specific mortality rates for females than males produced higher age-specific female-to male sex ratios in the early adult years than in later years. Mortality generally increased with age in whites whereas the phenomenon of an accentuation and decline during the early and middle adult ages was seen in blacks, particularly females. Analysis of age-, sex-, race-specific rates using one measure of synergistic interaction, S, revealed substantial synergy between the effects of sex and race on mortality during the childbearing ages (S = 3.2, 95% confidence interval = 2.3--4.4).