Differences exist in patterns of labor force participation of urban poor whites, blacks, Puerto Ricans, and Mexican Americans. Young unmarried blacks of both sexes, older Puerto Rican women, and Mexican American women in all age categories are less likely to participate in the labor force than are whites in the corresponding groups. Some of the differences in participation may be explained by educational attainment, but this accounts for only a small amount of the variation; none can be explained by geographic factors. The subgroups respond to education and economic factors in different ways, which leads to the conclusion that labor force participation among the groups is heterogeneous. Additional research is needed to provide answers for the reasons for variation in labor force participation. (BC)