The essential oil from the leaves ofPiper betleL. Sagar Bangla cultivar has been found in vitro to be highly active against the growth of four keratinophilic fungi,Arthroderma benhamiae, Microsporum gypseum, Trichophyton mentagrophytes, Ctenomyces serratusand five pathogenic Aspergilli. Bacterial organismsBacillus subtilis, B. pumilus, Staphylococcus aureus, Salmonella typhiandVibrio choleraewere also found to be susceptible to the oil. The essential oil was also found to be more effective against tapeworms(Taenia solium)and hookworms(Bunostomum trigonocephalum), than the synthetic anthelmintics piperazine phosphate and hexyl resorcinol. The results presented lend some credibility to some of the reported applications ofPiper betlein the Indian system of medicine.