The antimicrobial activity of the sequential n-hexane, acetone and 50% aqueous methanol extracts of leaves, stem bark and roots of four species of medicinal plants, Cassia sieberiana DC. (Leguminosae), Haematostaphis barteri Hook. f. (Anacardiaceae), Mitragyna inermis (Willd.) O. Kuntze (Rubiaceae) and Pseudocedrela kotschyi (Schweinf.) Harms (Meliaceae), from Ghana were tested against Bacillus subtilis, Pseudomonas syringae and Cladosporium herbarum using TLC direct-autobiographic methods. Extracts from leaves, stem bark and roots of the four species gave a positive result against at least one test organism. Twelve of the 36 extracts were active against B. subtilis, four extracts were active against P. syringae and six were active against C. herbarum. Preliminary chemical analysis revealed the presence of flavonoids, stilbenes and alkaloids. This is the first report of a stilbene from the Anacardiaceae.