A large proportion of the population in Uganda still relies on the use of plant extracts for treatment of various ailments. This study tested the claimed efficacy of some plants in the treatment of measles. In vitro antiviral assays were performed on extracts of two medicinal plants (Warburgia ugandensis and Zanthoxylum chalybeum) using measles virus (Edmonston and Swartz strains) as the test organisms. The assays performed were the neutralisation tests and the plaque reduction assays. Of the two plants Z. chalybeum had demonstrable in vitro antiviral activity in the seed extracts (titer reduction factor [TRF]: 100, for the ethanolic extract). The in vitro antiviral activity of the seed extracts was demonstrated to be due to compound 27-135D (TRF=1000), which was characterized by (1)H-NMR spectroscopy as the alkaloid skimmianine. Skimmianine had minimal toxicity to VERO cell lines. The petroleum ether extracts and the ethanolic extracts of Warburgia ugandensis had no inhibitory effect on cytopathic effect (CPE) formation, especially at the maximal non-toxic dose (MNTD). The extracts of W. ugandensis were highly toxic to VERO cell lines. The TRF values for the stem bark extracts of W. ugandensis were: water extract, 10; ethanolic extract, 1; fraction 27-163D, 100., which were regarded to be too low. Seed extracts of Z.chalybeum therefore probably cure measles due to the antiviral effect of skimmianine. It is not clear how extracts of W. ugandensis produce a beneficial response in measles disease, if at all.