The high antitumour activity against murine P388 lymphocytic leukaemia (3PS) of extracts of Pimelea plant species (Thymelaeaceae) has been attributed to daphnane orthoesters [1 3]. Several chromatographic fractions of the Pimelea extracts were found to exhibit much higher activity than could be accounted for by the amounts of daphnane orthoesters present. These fractions were found to be mixtures of l-monolinolenoylglycerol (2) and traces of daphnane orthoesters. Synthetic 2 (but no other mono- or diglycerides tested) was shown to potentiate strongly, in a dose-dependent fashion, the 3PS activity of the pure daphnanes gnidimarcin (1 c) [4] (isolated from P. ligustrina [2]) and Pimelea factor P2 (1 b) [1, 3] at levels which did not give significant activity for the daphnanes alone. This effect was enhanced if 2 peroxidized with air at 40 ~ was used. 2 and peroxidized 2 were inactive themselves and did not affect the activity of the anticancer drug, vincristine, in 3PS. This is the first report of the existence of a natural product which specifically potentiates the activity of antitumour agents present in the same plant. Bacillus subtilis is sensitive both to carbenicillin and kanamycin. However, as the antibiotic concentrations are increased, a point is reached at which bacterial growth reappears, provided that penicillinase (fl-lactamase) is present in the medium. We have demonstrated a hitherto undescribed activity of penicillinase, the inactivation of kanamycin in the presence of carbenicillin.