Lycorine, an Amaryllidaceae alkaloid, is a powerful inhibitor of growth in higher plants and algae. Thirty-one strains of yeasts, belonging to different genera and species, were screened to study the effect of lycorine on their growth. The strains were incubated at 25 degrees C in a 2% glucose medium with different concentrations of lycorine (10, 50 and 100 microM), and their growth after 72 hours was evaluated. Most of the strains showed no sensitivity to lycorine. However, in Schizosaccharomyces pombe (IMAT-V Pbx) and Aureobasidium pullulans (DBV A77) lycorine significantly inhibited growth (59-73%), while, on the contrary, in Saccharomycopsis fibuligera (DBV 3812) and Cryptococcus terreus (CBS 1895) it was clearly stimulated (76-140%). The fact that lycorine inhibits growth in some yeasts while it stimulates it in others means that neither of the two previously formulated interpretations on the molecular mechanism of action of alkaloid can explain all cases. In other words, it does not seem that lycorine just inhibits protein synthesis, as claimed by Kukhanova et al. (1983), nor, on the other hand, do the data presented here prove that lycorine specifically inhibits ascorbic acid biosynthesis (Arrigoni et al., 1975). We must now check the ability of yeasts to split lycorine and study whether yeasts do actually have an ascorbic acid system.