The factors affecting oil yield and quality of essential oils from Dalmatian sage (Salvia officinalis L.) are analyzed. Distillations of oils from individual plants and GC analyses revealed the presence of three chemotypes with different proportions of alpha- and beta-thujone (alpha/beta 10:1, 1.5:1, and 1:10). Different accessions could also be classified as having high (39-44%), medium (22-28%), or low (9%) total thujone contents. Flowering parts of S. officinalis had higher oil contents (1.6 versus 1.1%) and beta-pinene levels (27 versus 10%) than leaves and lower thujone levels (16 versus 31%). Major seasonal changes were found in the composition of oil distilled from a flowering type of Dalmatian sage, but oil yields from healthy, established plants did not vary greatly. Total thujone levels were lowest (25%) around flowering in spring and summer, so autumn or winter was the best harvest time to obtain oils with high thujone levels.