The hoatzin is a folivore bird with crop microbial fermentation. We studied plants selected by the hoatzin as food and their toxicity, in relation with non-selected plants. Toxicity of dietary and non dietary plants was tested in bioassays of ethanol plant extracts on eukaryote cells lines and on crop bacterial cultures. The hoatzin selected young leaves and soft tissues from the plants regardless their abundance or their cytotoxic activity. The most cytotoxic dietary plants were from Pithecellobium and Pterocarpus genera, and crop bacteria were less inhibited by plant extracts if the corresponding plants were consumed.