A dichloromethane extract of Hakea amplexicaulis was found to cause strand scission of phi X174 replicative form DNA in the presence of Cu(II). Bioassay-guided fractionation of this extract afforded five compounds capable of mediating DNA relaxation. Structure determination of the active principles indicated that they were 5-tridecylresorcinol (1), 5-pentadec-cis-8-enylresorcinol (2), 5-heptadeca-8,11-dienylresorcinol (3), 5-pentadecylresorcinol (4), and 5-heptadec-cis-8-enylresorcinol (5). As noted previously for compounds in this structural series, DNA cleavage was enhanced significantly by incubation under (alkaline) conditions known to promote oxygenation of the parent compounds on the aromatic nucleus.