Organ culture of rat lateral prostate was performed in the presence of testosterone and cadmium. Maintenance of epithelial cells did not occur even in the presence of the androgen, but basal cells were stimulated and replaced original epithelium. Testosterone alone caused a partial differentiation of these basal cells. Cadmium alone was found to enter the epithelial and basal cells and subsequently cause necrosis. The metal was subcellularly located in the nucleus and within cytoplasmic organelles. Cadmium appears to compete with zinc in cultured lateral prostate and affects the differentiation and maintenance of the epithelial growth.