Fourteen aristolochic acids are known, two of which have been isolated as the methyl esters. Aristolochic acids are often accompanied by aristolactams, twelve of whom have been obtained from natural sources.Aristolochic acids have been found only among the Aristolochiaceae, as well as in butterflies that feed on such plants. The botanical range of the aristolactams is somewhat broader. Most of them are still found in the Aristolochiaceae, although there are also well authenticated reports of their occurrence in some members of the Annonaceae, llenispermaceae and Monimiaceae.A singular structural feature of the aristolochic acids as well as the aristolactams has been that whenever an oxygenated function was present in the bottom aromatic ring, this substituent was situated at either C-6 or C-8. Similarly, when two substituents were present, these could be found only at C-6 and C-8. Very recently, however, 7-hydroxy- (6) and 7-methoxyaristolochic acid-A (9) have been reported which are oxygenated at both C-7 and C-8. Another unusual species is debilic acid (ll), which is strictly speaking a homoaristolochic acid since it incorporates a carboxymethyl sidechain at C-1.Even though aristolochic acids and aristolactams are non-basic, they are nevertheless classified as aporphinoids since their respective skeletons A and B bear a distinct similarity to that of the aporphines. 'The chemistry, biogenesis and pharmacology of the aristolochic acids and aristolactams has been reviewed.* Uv wavelengths are in nm, ir frequencies in cm-1, and nmr chemical shifts in ppm on the 6 scale. Melting points are in degrees centigrade.