1,8-cineole defines a typical chemotype of thymus vulgaris l. in iberian peninsula. this compound has a wide range of potentially useful bioactive properties. in order to study the influence of drought stress in the essential oil (eo) composition of this chemotype, sixty plants from six wild populations of eastern iberian peninsula were distilled and analyzed by gc and gc/ms. the harvest dates (may and august) were selected in such a way that the typical summer drought in mediterranean climates was the critical factor affecting eo composition. despite the high intrapopulational variability, significant increases of 1,8-cineole were found after the drought period (21.8%-43.2%, in may, up to 42.6%-68.5% in august). on the other hand, individuals from one of the populations showed different profiles rich in linalool and camphor or sesquiterpenoid compounds, such as -cadinol.