the essential oil composition of acorns calamus (sweet flag) leaves collected in lithuania at different growing phases was examined by gc and gc/ms. rhizome oils of a. calamus, having been more thoroughly investigated, were used for comparison purposes. the content of the oil in dried sweet flag rhizomes was 1.20+/-0.12% and in the leaves, depending on the vegetation phase, was from 0.56-1.01%. ninety-one constituents were positively or tentatively identified in the oils-66 in the leaves and 55 in the rhizomes. possible formation of calacorene hydrates is suggested for the first time on the basis of mass spectral data. beta-asarone [(z)-asarone] was the major constituent in the leaves (27.4-45.5%), whereas acorenone was dominant in the rhizomes (20.86%) followed by isocalamendiol (12.75%). a higher content of some aliphatic and oxygenated monoterpenes was found in oils of the leaves at their earliest growth phase (may), while the beta-asarone content was at its lowest level.