Proteins from secretions or homogenates of mice seminal vesicles were analysed by polyacrylamide gel electrophoresis. In homogenates about 15 bands were differentially induced with molecular weights (MW's) of 12, 13, 14, 15, 15.5, 71, 120 and 140 kD, or repressed molecular weights of 12.5, 14.3, 28, 30, 53, 73, 90-105 kD). The effects of castration were reversed by testosterone and dihydrotestosterone but not by oestradiol, progesterone or corticosterone. When the androgen-dependence of proteins was investigated using radioactive methionine the protein spectra showed that about 12 bands with molecular weights of 13, 13.7, 14, 15, 15.5, 16, 20.5, 24, 37, 38.5, 56, 68, 96 and 180 kD were differentially induced or repressed by androgens. Of the induced proteins, those with low molecular weight (12-15.5 kD) were accumulated in significant amounts between 20 days and 30 days, coincident with the pubertal increase of androgens in the seminal vesicles. Those induced proteins with high molecular weight (71, 120 and 140 kD) appeared between 40 days and 60 days. The androgen-repressed proteins were strongly evident in immature males, but disappeared after day 40.