To examine the androgen receptor in androgen-dependent and-independent tumor immunohistochemically, an indirect immunofluorescence study with an antibody to human androgen receptor was performed. Shionogi Carcinoma 115 (SC 115) cells are an androgen-dependent mouse tumor, but the growth is sustained without androgen when fetal bovine serum is added to serum-free medium. Cells obtained from successive culture (A (-) X cells; X is generations after removal of androgen) were androgen-independent but showed binding to androgen. SC 115 cells, A (-) cells and CS 2 cells which are the other androgen-independent cells derived from SC 115, were used in the study. The androgen receptor (AR) in SC115 cells was stained as small-sized oval granules localized in the nucleus, and the number of the granules was 10-20 per cell. Removal of testosterone for one day as well as one week did not change the size of the AR, but some of the AR in A (-) 10 cells and in generations thereafter appeared to be large. Other small ones were similar to that in SC 115 cells. The nuclear location of the AR did not change in A (-) cells. The ratio of cells containing large AR to the total number of cells increased with each generation after the removal of testosterone from the culture. The addition of testosterone to the culture changed the AR in A (-) 40 cells to small ones, but did not influence the form of the AR in A (-) 60 cells. The AR in CS 2 cells had a similar appearance to that in A (-) 60 cells and did not change the form by addition of testosterone. These results suggest that AR in the functional state is small and oval in shape, and long term removal of testosterone gradually change the AR to a large one. The return of the large form of AR to a small one occurs within a limited period in the absence of androgen, but thereafter no reversibility is noticed.