abstract the chemical composition of the oils from two endemic and rare taxa of the genus origanum l., i.e o. calcaratum juss. = o. tournefortii aiton and o. scabrum boiss. et heldr., from greece, were investigated by gc and gc/ms. twenty-two compounds were identified into the oil of o. calcaratum, representing 98.0% of the oil composition. the main compounds were p-cymene (18.1%), -terpinene (9.6%), thymol (42.8%), carvacrol (12.9%) and isocaryophyllene (4.7%). in the oil of o. scabrum, 28 compounds were identified, representing 98.0% of the oil composition. the main compound was carvacrol (66.7%), while p-cymene (7.8%), -terpinene (3.6%), caryophyllene oxide (2.1%) and manool (2.7%) were found in large amounts. the oils were investigated for their antimicrobial activity against gram-positive, i.e., staphylococcus aureus, s. epidermidis and gram-negative, i.e., escherichia coli, klebsiella pneumoniae microorganisms.