A minute amount of the new kainic acid-like amino acids, acromelic acid A (ca. 110 ug) and B (ca. 40 ug), was isolated from the poisonous mushroom Clitocybe acromelalga and their structures were inferred to be 1 and 2_ respectively by spectral analyses. The poisonous mushroom Clitocybe acromelalga Ichimura is found in Japan only and exhibits unique symptoms similar to erythromelalgia or acromelalgia. Its remarkable physiological properties prompted us to study chemical constituents of this fungus. 1) Fractionation guided by the lethal effect on mice led to the isolation of a very minute amount of the amino acids structurally related to kainic acid and domoic acid. 2) We describe in this communication the isolation and characterization of these compounds, named acromelic acid A (I) and B (2). acromeiic acid A J, acromelic acid B 2 Water extract of 16.2 kg of fresh fruiting bodies was subjected to acetone precipitation, dialysis of the precipitate and the dialysate was then chromatographed successively on charcoal (2.5-5% EtOH), Amberlite IR-45 (HC02-form, lo-20% HC02H), paper electrophoresis (pH 4.6, +90 mm) to give 52 mg of crude toxic fraction. Crude acromelic acids A and B were separated from the poisonous fraction by cellulose TLC (nBuOH/HCO,H/H,O=6/1/2, Rf 0.41 and 0.28 respectively), and purified by cellulose TLC (nBuOH/AcOH/H20=4/1/5) and finally by paper electrophoresis (pH 4.6). Amounts of purified acids A and B were about 110 ug and 40 ug respectively. Both compounds showed yellow coloration with ninhydrin, strong blue fluorescence under UV light and behavior of a strong acid comparable to cysteic acid on chromatography. Due to the limited sample quantity, the spectral data available were 'H NMR and UV spectra only.3) The formulas l_ and 2, however, could be inferred from these data comparing them with those of related compounds. The 'H NMR spectra of both l_ and L (360 MHz, D20, DSS standard) were consisted of an pattern due to aromatic protons and signals ascribable to three methine and two methylene 939 AB groups.