Abstract Aminophosphonic acids and related derivatives have previously attracted attention as possible plant-growth regulators and for their potential as herbicides. We have now shown that a number of amino-alkanephosphonic acids of the general type (HO)2P(O)CR3R4 (CH2)n NR1R2have useful fungicidal activity, eapecially for agricultural use (1). Arising from extensive laboratory tests and field triala α-aminopropanephosphonic acid (code number PNL 62) has been developed for commercial application under the draft common name ampropylfos. This new pesticide is especially useful primarily as a seed-dresaing agent for the control of Drechslera teres. Both R- and S-isomers are active. The compound shows no phytotoxic activity and is of very low mammalian toxicity (LD50 > 5000 mg kg−1). Within the series of aminophosphonic acids investigated, activity was greatest when the amino group is in the alpha position. Activity decreased with increasing branching in the alkyl chain and was removed by the presence of vari...