We show field and experimental evidence that introduced herbivores and soil degradation strongly influence the distribution of introduced herbs in the Chilean matorral. In the field, the relative abundance of introduced species was higher on sites grazed by livestock and on very poor soils. Two factorial experiments assessed the effects of rabbit grazing, nutrient addition, and fire. Native grasses were more sensitive than introduced grasses to grazing. With nutrient addition, native grasses increased while introduced grasses tended to decline. Fire had no significant effects on our experimental plots. We discuss several factors that might explain why alien herbs are more successful in the Chilean matorral than in the Californian chaparral.