1. It has been reported that the first intron of the renin gene of the spontaneously hypertensive rat (SHR) is shorter than that of the Wistar-Kyoto (WKY) rat, suggesting a role for this difference in the development of hypertension. 2. The genealogy of some Australian SHR colonies has raised doubts about its similarity to the Japanese, American and European colonies. 3. The polymerase chain reaction (PCR) technique has been used with primers identical to the flanking region of the first intron of the renin gene to determine its length in SHR, WKY and Sprague-Dawley (SD) from an Australian colony. 4. The size of the first intron of the renin gene in SHR, WKY and SD was found to be approximately 3870, 4550 and 5000 base pairs, respectively, results which agree with those previously published. 5. It was concluded that the first intron deletion, and its size, has been conserved in an Australian SHR colony.