This work studies the effects of suramin on the growth and morphology of cell strain U285, obtained from human prostate hypertrophic tissue and cultured in vitro. The FRAME cytotoxicity test was performed to evaluate the inhibition of growth induced by suramin. Cells were exposed to suramin at the time of seeding and 24 hours later; neutral red was added with and without suramin. An optical microscope connected to a computer-aided system and a scanning electron microscope were used to study morphological changes induced by suramin. Growth inhibition depends on drug concentration and exposure period. Moreover, the effect of suramin on neutral red uptake is reversible. Suramin 1,000 microM causes the cells to become spheroid, and they fail to form a monolayer. Our data indicate that the addition of suramin during the lag phase decreases the rate of cell proliferation.