It is commonly assumed that the adverse effect of plant residues on crop yields is largely, or partly, due to phytotoxic compounds leached from these residues or produced by their decomposition, and it has been suggested that the phytotoxic compounds responsible for reduced crop yields are aliphatic acids such as acetic acid, butyric acid, and propionic acid. To test the validity of this hypothesis, we studied the effects of different amounts of acetic acid, butyric acid, and propionic acid on seed germination and seedling growth of corn(Zea maysL.), barley (Hordeum vulgareL.), and wheat(Triticum aestivumL.) in soils. The data obtained showed that the aliphatic acids tested had adverse effects on seed germination and seedling growth only when the amounts applied were much greater than the amounts reported to occur in soils treated with plant residues. We conclude that the adverse effect of plant residues on crop yields is not due to aliphatic acids derived from these residues.