The effects of ethylene on such processes as fruit ripening, abscission, and senescence are well known. Ethylene also participates in a variety of responses in the root zone. For example, ethylene affects root extension, root hair development, aerenchyma formation, and root gravitropic responses. We here present evidence for the involvement of ethylene in a variety of root developmental responses to nutrient deficiency and other stresses. Using contrasting genotypes of common bean (Phaseolus vulgaris), we show that ethylene participates in the change in basal root angle in response to phosphorus deficiency. In Arabidopsis thaliana, we show that ethylene and phosphorus deficiency increase root hair density via separate pathways. Using an ethylene-insensitive genotype of petunia (Petunia hybrida), we show that preventing ethylene action increases susceptibility to disease, especially in plants already subjected to nutrient stress. We suggest that ethylene participates in the signaling processes for some, but not all, root developmental responses to edaphic stresses.