A peptide associated with antiviral activity, isolated from the high plant Melia azedarach L. was purified and partially characterized. Crude extracts of green leaf were purified by gel filtration on Sephadex G-100 followed by DEAE-Sephadex A-25. After column chromatography purification, an active compound II was revealed by elution with chloroform: methanol (95:5). Further analysis using thin-layer chromatography (TLC) revealed three components. With Rf 0.37 (component II), one of these had the highest antiviral activity as determined by inhibition of VSV replication. Compound II (meliacine) also inhibited the in vitro replication of PrV, HSV-1, HSV-2, Junin virus, Tacaribe virus, and Sindbis virus. Chemical analysis showed the antiviral compound to be a cyclic peptide with a MW 2200-2300 containing only aliphatic aminoacids. An unusual feature of the peptide was the presence of a single glucose unit that could be released by mild alkaline treatment which caused degradation of the peptide.