Hybridohistochemistry was applied for the detection of renin mRNA in the mouse kidney with a digoxigenin-labeled probe, synthesized as the sense and antisense RNAs from Ren-1 cDNA in the presence of digoxigenin-dUTP. Renin mRNA was detected in the juxtaglomerular cells located in the vicinity of the glomerular vascular poles of the kidney using the digoxigenin-labeled antisense RNA as a probe. Using the sense RNA as a probe, no signal was detected anywhere. In neighboring serial sections, the same cells reacted immunohistochemically to rabbit anti-mouse submandibular gland renin serum as in hybridohistochemistry. As we used the probe labeled with digoxigenin as a non-radioisotopic marker, there was no need for special handling other than that in immunohistochemistry. It was concluded that the simple procedure given in the present study is useful for the detection of mRNA.