Transcription of at least one member of the potato prp1 gene family, prp1-1, is activated at early stages of potato infection with the late blight fungus Phytophthora infestans. In this paper we present evidence that mRNA encoded by prp1-1 does not accumulate in response to abiotic environmental cues which stimulate transcription of other defence-related genes. Regulatory elements were identified in the 5' terminal region of prp1-1 by assaying the expression pattern of chimeric promoter/beta-glucuronidase gene constructs in transgenic potato. A 273 bp fragment comprising the promoter sequence between positions -402 and -130 was sufficient for rapid and strictly localized transcriptional activation at infection sites during the development of late blight disease. Like the native promoter, this truncated promoter did not mediate transcriptional activation in response to other abiotic stimuli. The use of the identified regulatory region to generate conditional mutations selectively at infection sites is discussed.