In vitroscreening of the crude extracts of some Brazilian coastal seaweeds for cytotoxic activity against a cultured human melanoma cancer cell line using the sulphorhodamine B assay was performed. The crude dichloromethane:chloroform extract ofStypopodium zonaleshowed good cytotoxic activity against the C32 cell line. The crude acetone extract and aqueous phase ofLobophora variegatadid not show any activity, but semi-purified fractions XAD LOB I and II could inhibit the growth of melanoma cells. The crude acetone extract ofCaulerpa racemosashowed some cytotoxicity, but caulerpin isolated from this extract did not show any such activity. The crude acetone extract ofSpatoglossum schroederiwas not able to inhibit the growth of C32 melanoma cells. Copyright © 2006 John Wiley & Sons, Ltd.