Molecular and cellular effects of two groups of antiproliferative agents, natural brassinosteroids and their synthetic derivatives, were examined in different adherent human cancer cell lines (MCF-7, MDA-MB-468) and in primary endothelial cells (HUVEC, HMEC-1). Their effects were studied by classical biochemical methods (SDS-polyacrylamide gel electrophoresis and immunoblotting, indirect immunofluorescence analysis, flow cytometry, caspase activation assay) and by angiogenesis assays in vitro (proliferation, migration, tube formation). Brassinosteroids and their derivatives can inhibit the growth of several human cancer cell lines and inhibit angiogenesis-like behaviour of primary endothelial cells in vitro.Molecular and cellular effects of two groups of antiproliferative agents, natural brassinosteroids and their synthetic derivatives, were examined in different adherent human cancer cell lines (MCF-7, MDA-MB-468) and in primary endothelial cells (HUVEC, HMEC-1). Their effects were studied by classical biochemical methods (SDS-polyacrylamide gel electrophoresis and immunoblotting, indirect immunofluorescence analysis, flow cytometry, caspase activation assay) and by angiogenesis assays in vitro (proliferation, migration, tube formation). Brassinosteroids and their derivatives can inhibit the growth of several human cancer cell lines and inhibit angiogenesis-like behaviour of primary endothelial cells in vitro.