In a search for an analogue of AAL-toxin with high phytotoxicity and low mammalian toxicity, aminopentols [(AP1), hexacetyl AP1 and N-acetyl AP1], and nine analogues (1-9), were tested for toxicity to duckweed (Lemna pausicostata), susceptible tomato (asc/asc) leaf discs, black nightshade leaf discs and mammalian cell lines, including dog kidney (MDCK), rat liver hepatoma (H4TG) and mouse fibroblasts (NIH3T3). These were compared with AAL-toxin and fumonisin B1 (FB1). Analogue 9 at 10 microM increased cellular leakage and chlorophyll loss from both tomato and black nightshade leaf discs. The diester 9 was the most active in the duckweed bioassay, but it was much less toxic to MDCK and H4TG cells with an IC50 of 200 microM compared to 10 microM for FB1. Analogue 9 and FB1 showed similar low toxicities (IC50 = 150 microM) to NIH3T3 cells. Among the substances tested, only analogue 9 had significant phytotoxicity and low mammalian toxicity, indicating some potential for development of safe and effective natural herbicides.