The Dunning R-3327 rat prostatic adenocarcinoma and its sublines have been developed as a model system to study prostate tumor progression. We have used this system to study the changes in androgen receptor (AR) and AR mRNA expression which occur during tumor progression from androgen dependent to androgen independent growth. Dorsal prostate and all tumor sublines contained a 10-kilobase AR mRNA on Northern blot analysis. The levels of AR mRNA in each subline compared to dorsal prostate (100%) were: H (75%) greater than G (48%) greater than HI (25%) greater than HI-F = AT-1 = AT-3 = MAT-Lu = MAT-Ly-Lu = less than 5%. Immunocytochemistry showed AR predominantly in acinar epithelial cells of dorsal prostate and the androgen sensitive H subline. In the H subline, both acinar epithelial cells and locally invasive adenocarcinoma cells within the stroma showed positive immunostaining. The androgen responsive, anaplastic G subline also showed strong positive immunostaining. The androgen resistant AT-1 and MAT-Lu sublines lacked immunostaining for the AR. Steroid autoradiography revealed a similar cellular distribution of AR. These data suggest that in the Dunning system the loss of androgen binding and responsiveness is primarily due to selective changes in gene expression and not to gene rearrangements or posttranscriptional or translational modification of the AR mRNA or protein.