Changes in gene expression induced by mechanical injury and heat shock were studied by comparing the expression of several stress-responsive gene families in potato tubers. The steady-state levels of mRNA-encoding ubiquitin, HSP70, and phenylalanine ammonia-lyase (PAL) increased and patatin transcript levels decreased within 45 minutes of impact injury. Nuclear runoff assays were used to demonstrate that the changes in steady-state transcript levels were due, at least in part, to changes in the rate of transcription for these genes. The observed changes in transcript levels were confined to the injured portion of the tuber. Treatment of tubers with exogenous ethylene elicited the same changes in the steady-state transcript levels as impact injury, indicating a potential role for this hormone in the injury-induced regulation of these genes. Two other forms of physical stress, heat shock and cutting injury, resulted in patterns of gene expression that are different from those induced by impact injury. The stress-induced regulation of these four gene families is complex, even though several characteristics of their expression are similar.