Based on ethnopharmacological literature, 17 species of medicinal plants used in the traditional medicine in Papua New Guinea were collected. Extracts of different polarities were tested in a preliminary biological screening for their antimicrobial (Escherichia coli, Bacillus subtilis, Micrococcus luteus and Penicillium oxalicum) and molluscicidal activity against Biomphalaria glabrata as well as for their toxicity to brine shrimp. The pretreated plant extracts were also investigated for their ability to inhibit protein kinase C and tyrosine-specific protein kinase of epidermal growth factor receptor. Furthermore, all plants were screened for the presence of alkaloids.