TLC analysis of the methanolic extracts of Boenninghausenia albiflora Reichb. revealed the presence of several acridone alkaloids in the roots [1,2]. Since no acridone alkaloids have been reported from this plant before, solvent-solvent fractionation was undertaken for the separation of these compounds [3]. In a preliminary communication [4] the isolation of three of these yellow alkaloids was described. One of them (Br5) was identified as 1-hydroxy-N-methylacridone (5), the two remaining one were tentatively designated Br2 and Br6. In the present paper we report on the characterisation of these two compounds and on three further compounds isolated from the same extract. Two of them (Br2 and Br6) were isolated from the benzene soluble fraction of the extract (see Experimental), the third one (Br7) was separated from the ethyl acetate soluble fraction. Two (Br2 and Br6) were identified by direct comparison with authentic samples as rutacridone (1) and noracronycine (2) respectively. The alkaloid Br4, C13H9O2N (M+ at m/e 211), in its NMR spectrum indicates the presence of a chelated C-1-OH group and of seven aromatic protons. This region shows a striking similarity to that of N-methylacridone. Thus structure 4 (1-hydroxyacridone) can be formulated and this is confirmed by the conversion of 4 to 1-hydroxy-N-methylacridone (5) via methylation. The molecular ion of Br7 (m/e 241) indicates a molecular formula C14H11O3N. The NMR spectrum exhibits two singlets at 3.93 and 14 (C-1-OH) ppm. The assignment of the first mentioned signal to a methylimino-group is deducible from its downfield shift in trifluoroacetic acid. The brown colour reaction of Br7 with alcoholic ferric chloride [4] is characteristic for a free phenolic OH-group. An ABX-system analogous to those of Br2 and Br4 shows three adjacent protons in position 2,3 and 4. The remaining signals of the other three protons must be assigned to the second benzene ring. On this basis, structure 6 is favoured. This structural proposal was confirmed by synthesis [5]. Compound Br8 is slightly water-soluble. Its IR spectrum exhibits very intense OH bands at 3400 and 1060 cm-1 indicating its polyhydroxylated nature. Acidic hydrolysis of Br8 yielded glucose and a yet unknown acridone aglycone. Thus compound Br8 must be an acridone glucoside. To our knowledge, this is the first report on the isolation of 1-hydroxyacridone and of 1,7-dihydroxy-N-methylacridone (6) from a plant species; compound Br8 is probably a new natural acridone alkaloid, too. The most interesting feature of our results is the joint occurrence of rutacridone (1) and noracronycine (2) in the same plant. To our knowledge Boenninghausenia albiflora is the second rutaceous species known to contain both furanoid and pyranoid derivatives in the acridone series. The only other species containing both types is Atlantia ceylanica; either furanoid or pyranoid acridones occur in other species, e.g. Acronychia baueri, Glycosmis pentaphylla, Atalantia monophylla and Ruta graveolens [6-8].