N-nitroso-N-ethylurea (NEU) has been used as a mutagen to generate a range of plants of feverfew,Tanacetum parthenium, with altered morphologies and growth habits, to study the quantitative patterns of secondary metabolism in this medicinal species. Morphological and albino mutations were observed in a proportion of plants grown invitrofrom seeds treated with 5 mM NEU. Selective micropropagation of variegated and semi-chlorophyllous lines led to the isolation of normal green, variegated mosaics, semi-chlorophyllous and true albino lines, together with shoots independently exhibiting abnormal growth. Differences in leaf photosynthetic pigment contents of such axenic cultured shoots were assessed spectrophotometrically, with mean chlorophyll concentrations in albino and semi-chlorophyllous tissues of 6% and 34%, and carotenoid concentrations of 8% and 43%, respectively, of mean values in normal green control leaves. HPLC assessments of selected NEU-treated lines for parthenolide, the major bioactive compound in feverfew, indicated that mean (± s.d.) concentrations were consistently lower (P < 0.005) in albino leaf explants (0.52 ± 0.11% dry wt; n = 5) than in normal green leaf tissues (1.85 ± 0.67% dry wt; n = 5). In contrast, some plant accessions, which displayed a chlorophyl;-deficient characteristic, manifested as a uniform, semi-chlorophyllous leaf type, contained exceptionally high levels of parthenolide (maximum 3.54 ± 0.64% dry wt; n = 9). Feverfew seeds exposed to higher concentrations of NEU (10 and 20 mM) gave dysfunctional seedlings, arrested at the cotyledonary leaf-stage; callus induction from the latter seedlings was also impaired.