Inbred strains of mice carry either one of two alleles for the Ren-1 gene on chromosome 1; Ren-1c or Ren-1d. The Ren-1d allele is found in association with a tightly linked duplicated locus, Ren-2. The relative accumulations of renin transcripts derived from each locus were found to differ between mice with one or two renin loci in three extra renal tissues, the adrenal gland, testis, and sex accessory gland tissue. We find that the two Ren-1 alleles exhibit characteristic expression patterns in these tissues. Using genetic analyses and an allele-specific dideoxynucleotide primer extension assay we have further characterized the expression differences in these tissues. The results suggest that the allele-specific expression patterns observed for the Ren-1 genes are regulated by closely associated sequences in cis.